Re: [Tutor] Shadowrun programs
Jack Cruzan wrote: I am on the other coast but I too am looking for a group to play Shadowrun with. With at least three people interested think we could either -- 1) Port or create a python based SRCG (useless python still has a challenge for a collaberative effort.) 2) Make a SR rpg (I was think of in the style of Rogue or net hack but could be something more in depth) 3) Fun and Profit! -err uhm something like it? My time is unfortunately limited. However, I am available for reviews, ideas, playtesting, etc. For the record, I am a Linux user so it would be nice if any GUIs used a cross-platform toolkit. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Clash of the Titans and Mundane Matters
Michael Powe wrote:
Clash of the Titans
snip constructor discussions
Pilgrim is pedantically correct but Alan's comment matches how most of
us think about it.
Mundane Matters
I'm having a hard time with classes in python, but it's coming
slowly. One thing that I think is generally difficult is to parse a
task into "objects." Here's an example: in Java, I wrote an
application to track my travelling expenses (I'm a consultant; this
tracking of expenses is the itch I am constantly scratching. ;-)
I've also written this application in a perl/CGI web application as
well.) It's easy to see the outline of this task: create an abstract
class for expense and then extend it for the particular types of
expenses -- travel, food, transportation, lodging and so forth. In
python, I guess I'd create a class and then "subclass" it.
while that is a valid approach, it is not how most of us would do it. By
subclassing you have to edit the code every time a new expense type is
added. Ever used MS Money or Quicken? Imagine if the type of each item
was a subclass. Use a string.
A similar problem occurs with my HTML-parsing routine that I brought
to the list recently. Use of HTMLParser was suggested. I've looked
into this and usage means subclassing HTMLParser in order to implement
the methods in the way that will accomplish my task. Conceptually,
I'm having a hard time with the "object" here. (The fairly poor
documentation for HTMLParser doesn't help.) Apparently, I'm creating
a "parser" object and feeding it data. At least, that's the closest I
can get to understanding this process. How I'm actually feeding data
to the "parser" object and retrieving the results are matters open to
discussion. I'll be working on that when I get another chance.
This counts the tags in a html file piped in on stdin.
#!/usr/bin/python
import sys, HTMLParser
class TagCounter(HTMLParser.HTMLParser):
def __init__(self):
HTMLParser.HTMLParser.__init__(self)
self.tags = {}
def handle_starttag(self, tag, attrs):
self.tags[tag] = self.tags.setdefault(tag, 0) + 1
if __name__ == '__main__':
counter = TagCounter()
for line in sys.stdin.xreadlines():
counter.feed(line)
counter.close()
print counter.tags
Finally, in terms of "understanding python," the question I keep
coming up against is: why do we have both functions and methods?
What is the rationale for making join() a string method and a os.path
function?
a method is a function bound to a class. Nothing super special.
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Re: [Tutor] Should this be a list comprehension or something?
Terry Carroll wrote: > My goal here is not efficiency of the code, but efficiency in my Python thinking; so I'll be thinking, for example, "ah, this should be a list comprehension" instead of a knee-jerk reaction to use a for loop. as Alan says, list comprehensions, like map should be used to generate new lists. What you should have thought was -- hmm, this looks like a job for reduce! def sumWater(w1, w2): total_mass = w1.mass + w2.mass numerator = (w1.mass * w1.temperature) + (w2.mass * w2.temperature) return Water(total_mass, numerator / total_mass) def CombineWater(WaterList): return reduce(sumWater, WaterList) if __name__ == '__main__': w1 = Water(50,0) w2 = Water(50,100) w3 = Water(25,50) print CombineWater2((w1,w2,w3)) Now, the sum_water function could also be folded into the Water class as an __add__ method if you like as someone else suggested. See, the problem with your old code was that the list walking and the summation were done by the same code. By pulling sumWater out you can test it separately. You could also pass different functions to CombineWater. And now, for the pedant in me. I would recommend against naming functions with initial capital letters. In many languages, this implies a new type (like your Water class). so CombineWater should be combineWater. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Should this be a list comprehension or something?
Brian van den Broek wrote: Sean Perry said unto the world upon 2005-01-27 02:13: And now, for the pedant in me. I would recommend against naming functions with initial capital letters. In many languages, this implies a new type (like your Water class). so CombineWater should be combineWater. Do you mean implies by the dominant coding conventions, or by language syntax? (Indulging the curious pedant in me.) In many OO languages, it is tradition to name types with capital letters (TFoo anyone?) and functions / methods with initial small then caps (camelCase). Haskell actually enforces this rule (nifty functional language). Python and it share a lot in common. (As an anti-example) Erlang enforces capital letters for variable names ONLY. A little odd and definitely takes some getting used to. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] rounding
Kim Branson wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Hi all, heres a quick one for you, I have a series of data that I am using dictionaries to build histograms for. I'd like to round the data to the nearest 10, i.e if the value is 15.34 should we round down to 10? and conversely rounding say 19.30 to 20. I'm thinking 15.5 and above would round up. Can anyone point me a at a quick and painless way of achieving this? def round10s(f): rem = f % 10 tens = int(f / 10) if rem >= 5.5: return (tens + 1.0) * 10.0 return tens * 10.0 if __name__ == '__main__': tests = [15.34, 15.54, 19.65, 2.34, 8.2, 0.0, 20.0] for i in tests: print "%.2f: %.2f" % (i, round10s(i)) yields 15.34: 10.00 15.54: 20.00 19.65: 20.00 2.34: 0.00 8.20: 10.00 0.00: 0.00 20.00: 20.00 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Dividing 1 by another number ?
Tony Meyer wrote: Dividing two integers will give you an integer (truncated) result: If you want '1/2' to give you 0.5 (throughout your script), you can do: from __future__ import division Notice that '//' (with or without the from __future__ import) will give you the integer result. or more simply, divide by 4.0 for rod and bore: (rod**2/4.0) what happens if rodarea is bigger than area? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Are you allowed to shoot camels? [kinda OT]
Liam Clarke wrote:
4) WHAT IS WITH THE STUPID SYMBOLS EVERYWHERE LARRY??!!
I'm not referring to the $ & @, I can see how they could be useful,
although with a list -
@dude = (1, 2, 3), to obtain the 2nd value I would expect $d = @dude[1],
not $d = $dude[1], that's counterintuitive also.
(I am an ex-perler gone clean. Been straight for 5 years now with only
the occasional work forced binges.)
Perl was designed by a linguist. He wanted it to act like human language
-- which is not very consistent.
That said, perhaps I can shed some light on the symbols.
Ever learned a Romance language? latin, spanish, french, etc? The
dollars and at signs can be thought of in relation to plural endings.
$foo --> dog
@dog --> a group of dogs
$dog[0] --> a dog in the group
So when you mean "the whole group" use the plural spelling and when you
want to refer to a member use the singular spelling. Likewise with other
parts of the language.
Personally, the thing that keeps me away from Perl is nested datastructures.
Python:
my_list = []
a_dict = {.}
b_dict = {.}
my_list.append(a_dict)
my_list.append(b_dict)
if my_list[0].has_key("foo"): print "Yes"
easy. Try that in Perl.
my @my_list; # remember those semicolons
my %a_dict, %b_dict;
push @my_list, %a_dict;
push @my_list, %b_dict;
if (exists $my_list->[0], "foo") print "Yes\n";
# yes, references required, in Perl ick.
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Re: [Tutor] Are you allowed to shoot camels? [kinda OT]
[EMAIL PROTECTED] wrote: Btw, I'm skeptical that the code below does what you want it to do. :-) that was kind of my point. In python I just type the obvious and it works. In Perl I have to muck with references, slashes, arrows and the like. Every time I have had to write a nested datastructure I have spent my time debugging that structure. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Ogg Tag Module recommendations
Miles Stevenson wrote: Can anyone recommend to me a Python module to work with ID3v2 tags in Ogg Vorbis files? I tried using the EyeD3 module, but it only supports mp3 right now, and I couldn't get the pyid3tag module to work reliably, or I'm just not understanding the documentation. I just need to retrieve all of the ID3v2 tag info from a collection of ogg files, store them in a file, and then insert them back into different ogg files. Anyone have a module/library they recommend? The Ogg guys actually made a wrapper for Python, pyvorbis I think it is called. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Are you allowed to shoot camels? [kinda OT]
Jeff Shannon wrote: However, Python doesn't need lambdas to be able to write in a functional style. Functions are first-class objects and can be passed around quite easily, and IIRC Python's list comprehensions were borrowed (though probably with notable modification) from Haskell. Note, it is haskell convention to name a list of objects with a plural. So xs -> list of x. haskell: [ x | x <- xs ] [ foo x | x <- xs, x > 2 ] python [ x for x in xs ] [ foo(x) for x in xs if x > 2 ] shaleh still mastering haskell, but loving it. Like python for functional languages. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Are you allowed to shoot camels? [kinda OT]
Alan Gauld wrote: Sean, what book/tutor are you using for Haskell? I learned it from "The Haskell School of Expression" which was OK but very graphics focused, I'd be interested in recommended second source on Haskell. as with Max I am reading Haskell: Craft of Functional Programming. I am about half way through it (have not got to Monads yet which are the mind benders). So far I really like it. Thought provoking examples and exercises. However there are no answers to the exercises. Which for a relative newbie to functional programming would have been nice. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with HTMLParseError
Peter Kim wrote: I'm using HTMLParser.py to parse XHTML and invalid tag is throwing an exception. How do I handle this? 1. Below is the faulty markup. Notice the missing >. Both Firefox and IE6 correct automatically but HTMLParser is less forgiving. My code has to be able to treat this gracefully because I don't have control over the XHTML source. ###/ /### what you want is to encapsulate check_for_whole_start_tag() in your own parser class. Call the parent's version, if it returns -1, do some fuzzy logic (well, maybe if I add a '>', now does it work?), and continue. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] SubClassing
Ismael Garrido wrote: Hello My code is like this: class Parent: def __init__(self, bunch, of, variables): self.bunch, self.of, self.variables = bunch, of, variables class Son(Parent): def __init__(self, bunch, of, variables, new): self.bunch, self.of, self.variables, self.new = bunch, of, variables, new What I want to know is, is there a better way to write Son class? One in which I don't have to copy&paste the parent's init? yep. call 'Parent.__init__(this, that)' then do 'self.new = new' def __init__(self, this, that, new): Parent.__init__(this, that) self.new = new ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] SubClassing
Ismael Garrido wrote: Sean Perry wrote: yep. call 'Parent.__init__(this, that)' then do 'self.new = new' def __init__(self, this, that, new): Parent.__init__(this, that) self.new = new Thanks. Though it should be: def __init__(self, this, that, new): Parent.__init__(self, this, that) #note self self.new = new been doing a bunch of C++ programming. C++ -> python I always forget about self. python -> c++ I always forget the semicolons (-: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] reading from stdin
Nick Lunt wrote: The way I did this was to use sys.stdin.readlines() to get the output from the pipe. Here is the program: [code] import sys, glob args = sys.stdin.readlines() # found on the net pat = sys.argv[1] for i in args: if (i.find(pat) != -1): print i, [/code] My question is am I getting the output from the pipe in the correct way ? The way Im doing it works (so far) but should I be doing it another way ? unless you want the output for some other reason, a more idiomatic way is: for line in sys.stdin.readlines(): # handle the line I tend to use xreadlines() which does not read the entire input at once. For stdin this make sense, you have no idea how much data will be piped in. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] reading from stdin
[EMAIL PROTECTED] wrote:
If I do:
$ ./produce.py | ./read.py
I get nothing for ten seconds, then I get the numbers 0 through 9, one per line.
What am I missing?
From the python man page:
-u
Force stdin, stdout and stderr to be totally unbuffered. On systems
where it matters, also put stdin, stdout and stderr in binary mode. Note
that there is internal buffering in xreadlines(), readlines() and
file-object iterators ("for line in sys.stdin") which is not influenced
by this option. To work around this, you will want to use
"sys.stdin.readline()" inside a "while 1:" loop.
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Re: [Tutor] slow html generation code
Luis N wrote: This code seems a little slow, is there anything in particular that jumps out as being not quite right. The idea is that a file is opened that contains path names to other files, that are appended and outputed into a directory of choice. I plan to move this off the filesystem into a database when the concept is worked out, maybe that will help. You are reading entire file contents into memory. Once with f.readlines() and then again with structure.read(). If these are somewhat large files that could definitely be a place for slowness. If nothing else, Python promises garbage collection to be done, but not when. So many of your files could be sitting in memory. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] regular expression question
Mike Hall wrote:
I'd like to get a match for a position in a string preceded by a
specified word (let's call it "Dog"), unless that spot in the string
(after "Dog") is directly followed by a specific word(let's say "Cat"),
in which case I want my match to occur directly after "Cat", and not "Dog."
I can easily get the spot after "Dog," and I can also get it to ignore
this spot if "Dog" is followed by "Cat." But what I'm having trouble
with is how to match the spot after "Cat" if this word does indeed exist
in the string.
. >>> import re
. >>> my_re = re.compile(r'(dog)(cat)?') # the ? means "find one or zero
of these, in other words cat is optional.
. >>> m = my_re.search("This is a nice dog is it not?")
. >>> dir(m)
['__copy__', '__deepcopy__', 'end', 'expand', 'group', 'groupdict',
'groups', 'span', 'start']
. >>> m.span()
(15, 18)
. >>> m = my_re.search("This is a nice dogcat is it not?")
. >>> m.span()
(15, 21)
If m is None then no match was found. span returns the locations in the
string where the match occured. So in the dogcat sentence the last char
is 21.
. >>> "This is a nice dogcat is it not?"[21:]
' is it not?'
Hope that helps.
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Re: [Tutor] regular expression question
Mike Hall wrote:
First, thanks for the response. Using your re:
my_re = re.compile(r'(dog)(cat)?')
...I seem to simply be matching the pattern "Dog". Example:
>>> str1 = "The dog chased the car"
>>> str2 = "The dog cat parade was under way"
>>> x1 = re.compile(r'(dog)(cat)?')
>>> rep1 = x1.sub("REPLACE", str1)
>>> rep2 = x2.sub("REPLACE", str2)
>>> print rep1
The REPLACE chased the car
>>> print rep2
The REPLACE cat parade was under way
...what I'm looking for is a match for the position in front of "Cat",
should it exist.
Because my regex says 'look for the word "dog" and remember where you
found it. If you also find the word "cat", remember that too'. Nowhere
does it say "watch out for whitespace".
r'(dog)\s*(cat)?' says match 'dog' followed by zero or more whitespace
(spaces, tabs, etc.) and maybe 'cat'.
There is a wonderful O'Reilly book called "Mastering Regular
Expressions" or as Danny points out the AMK howto is good.
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Re: [Tutor] working with new classes
C Smith wrote: ### class Ring(list): def __init__(self, l): self[:] = l self._zero = 0 def turn(self, incr=1): self._zero+=incr def __getitem__(self, i): return self[(i-self._zero)%len(self)] l=Ring(range(10)) print l l.turn(5) print l#same as original print l[0] #crashes python ### This is a classic mistake. l[0] --> l.__getitem__(l, 0), which you understand. However in __getitem__ you then call self[] which will just call __getitem__ again. and again. and again. The way out is to explicitly call the parent's __getitem__. def __getitem__(self, i): # list is out parent, call its method return list.__getitem__(self, (i - self._zero) % len(self)) ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Whats so good about OOP ?
Brian van den Broek wrote: 1) Namespace issues With procedural (or imperative -- don't know which is the right terms for non-OOP code which employs functions) code, you can have issues caused by namespaces. Just yesterday, someone on the main python list/newsgroup had code something like: procedural v. OO imperative v. functional In an imperative language you tell the computer what to do (imperative): "put 5 in X, use X in function foo, store foo's result in blah". The base component is an imperative statement. If you have not had an English grammar class recently imperative sentences are things like "You, bring me my supper". In a functional language, the base item is a function. foo(X(blah())) or for the lispy people (foo (x (blah))). You could do OO in a functional language. Haskell for instance has a concept of classes, user defined types, polymorphism, etc. The point is, these are two axes on the programming language chart. procedural, imperative -> C OO, functional -> OCaml (close enough anyways) ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Whats so good about OOP ?
Mark Kels wrote: Hi list ! I want to know whats so great in OOP... I have learned some of it, but I don't understand why everybody like it so much... Can anyone give me an example for a task that could be done only with OOP or will be much simpler to do with it ? Thanks in advance. Other commenters on this thread have covered OO fairly well. I have one clarification detail to add. In procedural code, you spend a lot of time micromanaging: put that there blah + quz is bar etc In OO code, you tell each object how to handle its data. Then your actual program just becomes a bunch of requests for objects to talk to each other. I know, you are thinking that is how your procedural code works today. But as you program, look at how much time you are telling the pieces what their jobs are and how much time you spend telling pieces to do their jobs. For further knowledge, read the Design Patterns book. It will seem like obvious, simple ideas you already know. It did for me. It is not until you start talking to other people that you realize what you learned. I am currently reading Holub's "On Patterns". He hammers OO ideas home pretty well. As Alan Gauld said, OO does not really start to shine until you reach a certain level of complexity. It takes most people quite a while to really get into the mindset. Take it slow, get it wrong, do it again (-: We all have. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] primes
Danny Yoo wrote: Here is one that's traduced... er... adapted from material from the classic textbook "Structure and Interpretation of Computer Programs": ## from itertools import ifilter, count def notDivisibleBy(n): ... def f(x): ... return x % n != 0 ... return f ... def sieve(iterable): ... nextPrime = iterable.next() ... yield nextPrime ... restOfPrimes = sieve(ifilter(notDivisibleBy(nextPrime), iterable)) ... for prime in restOfPrimes: ... yield prime ... primes = sieve(count(2)) primes.next() which is cool, until you try to use it (-: It dies at 999 primes due to an overloaded stack. Bummer. It is such a nifty implementation. I modified this version to follow it better. from itertools import ifilter, count def notDivisibleBy(n): def f(x): return x % n != 0 return f def sieve(iterable): nextPrime = iterable.next() print 'x', nextPrime yield nextPrime restOfPrimes = sieve(ifilter(notDivisibleBy(nextPrime), iterable)) for prime in restOfPrimes: print 'p', prime yield prime primes = sieve(count(2)) current = primes.next() count = 1 while current <= 20: print 'Prime:', current current = primes.next() count += 1 The output is (note this is each prime < 20): x 2 Prime: 2 x 3 p 3 Prime: 3 x 5 p 5 p 5 Prime: 5 x 7 p 7 p 7 p 7 Prime: 7 x 11 p 11 p 11 p 11 p 11 Prime: 11 x 13 p 13 p 13 p 13 p 13 p 13 Prime: 13 x 17 p 17 p 17 p 17 p 17 p 17 p 17 Prime: 17 x 19 p 19 p 19 p 19 p 19 p 19 p 19 p 19 Prime: 19 x 23 p 23 p 23 p 23 p 23 p 23 p 23 p 23 p 23 Not exactly efficient. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] primes
Pierre Barbier de Reuille wrote: def sieve( max ): max_val = int( sqrt( max ) ) s = Set(xrange( 4, max, 2 )) for i in xrange( 3, max_val, 2 ): s.update( xrange( 2*i, max, i ) ) return [ i for i in xrange( 2, max ) if i not in s ] just for grins, here is the same (mostly) code in haskell import Data.Set(elems, fromList, member, union) primeSieve :: Int -> [Int] primeSieve n = [ prime | prime <- [ 2 .. n ], not $ prime `member` nonPrimes ] where evenSet = fromList [4, 6 .. n ] xIncrements x = [ 2 * x, (2 * x) + x .. n ] maxVal = floor . sqrt $ fromIntegral n oddSet = fromList . concat $ map xIncrements [ 3, 5 .. maxVal ] nonPrimes = union evenSet oddSet fromList makes a list into a Set. [ x | x <- y, pred ] is analogous to Python's [ x for x in y if pred x ]. The '$' operator removes the need for parens. foo $ bar baz --> foo (bar baz) oh and '.' is the function composition operator. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Prepend to a list?
Jay Loden wrote: How can I prepend something to a list? I thought that I could do list.prepend() since you can do list.append() but apparently not. Any way to add something to a list at the beginning, or do I just have to make a new list? >>> a = [] help(a.insert) insert(...) L.insert(index, object) -- insert object before index ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Why is this not an error?
Hameed U. Khan wrote: This else is the part of the for loop. And the statements in this else will be executed if your for loop will complete all of its iterations. if you want this else with 'if' statement then remove the for loop. for instance: looking_for = 11 for i in range(0,10): if i == looking_for: handle_it(i) break else: print "Did not find", looking_for ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] primes (generator)
Gregor Lingl wrote: The following variation of your sieve, using extended slice assignment seems to be sgnificantly faster. Try it out, if you like. Here are the numbers: Primes 1 - 1,000,000 timing: extendedSliceSieve: 0.708388 seconds listPrimes: 0.998758 seconds karlSieve: 1.703553 seconds primeConciseOptimized: 5.133922 seconds setSieve: 7.564576 seconds primeConcise: 1644.683214 seconds --> 27 minutes 24 seconds if __name__ == '__main__': # setup timers as a list of tuples (name, timeit instance) results = [] longest = 0 for t in timers: result = t[1].timeit(1) longest = max(longest, len(t[0])) results.append((t[0], result)) results.sort(lambda x, y: cmp(x[1], y[1])) print "Primes 1 - 1,000,000 timing:" format_str = "%%%ds: %%f seconds" % longest for i in results: print format_str % i ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Filtering a String
Matt Williams wrote:
Dear List,
I'm trying to filter a file, to get rid of some characters I don't want
in it.
I've got the "Python Cookbook", which handily seems to do what I want,
but:
a) doesn't quite and
b) I don't understand it
I'm trying to use the string.maketrans() and string.translate(). From
what I've read (in the book and the Python Docs), I need to make a
translation table, (using maketrans) and then pass the table, plus and
optional set of characters to be deleted, to the translate() function.
I've tried:
#!/usr/bin/python
import string
test="1,2,3,bob,%,)"
allchar=string.maketrans('','')
#This aiming to delete the % and ):
x=''.translate(test,allchar,"%,)")
but get:
TypeError: translate expected at most 2 arguments, got 3
Please could someone explain this to me (slowly).
Here is an updated version.
#!/usr/bin/python
import string
test = "1,2,3,bob,%,)"
allchar = string.maketrans('','')
#This aiming to delete the % and ):
x = test.translate(allchar,"%,)")
print x
# end
x = test.translate() rather than x = ''.translate() is the key. You want
to call the translate method of the test string. Your code could have
worked by doing 'x = string.translate(test, allchar, "blah")' which uses
the translate function in the module named 'string'. Confusing because
the names are the same.
You received an error because ''.translate() only needs the table and
the deletechars string. I personally avoid empty string methods
(''.translate, ''.join, etc) because they can be visually confusing and
definitely confound the new python programmers.
A comment on style. Use spaces around assignments -- x=5 should be x = 5.
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Re: [Tutor] import statements in functions?
Marcus Goldfish wrote: Is there a convention to be considered for deciding if import statements should be included in a function body? For example, which of these two module layouts would be preferable: imports are cached. So once it is imported, it stays imported. The reason I consider the second form is that the module foo_special is only used by the code in specialFunction(), and detracts (IMHO) from understanding the rest of the code in the module. and this is a good reason why you would perform the import inside the function. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] OT - SQL methodology.
Liam Clarke wrote: Hi, This is a SQL query for the advanced db gurus among you (I'm looking at Kent...) After I've run an insert statement, should I get the new primary key (it's autoincrementing) by using PySQLite's cursor.lastrowid in a select statement, or is there a more SQLish way to do this? In the SQL books I've got, they always seem to have an optional select statement on the end of inserts/updates, and I was thinking maybe I could do it that way also, but I can't figure out a logical way of putting 'select primary_key from foo where primary_key value > every other primary_key value' select max(primary_key) from foo? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Looking for a Pythonic way to pass variable number of lists to zip()
Tony Cappellini wrote: I have a program which currently passes 6 lists as arguments to zip(), but this could easily change to a larger number of arguments. Would someone suggest a way to pass a variable number of lists to zip() ? well, I would have said "apply(zip, (l1, l2, l3, ...))" but apply has been deprecated in 2.3. So how about this? arg_list = [] # fill up arg_list zipped = zip(*arg_list) ? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Looking for a Pythonic way to pass variable
Shidai Liu wrote: On Tue, 22 Mar 2005 15:27:02 -0500, Bill Mill <[EMAIL PROTECTED]> wrote: zip(K, *L) [(100, 1, 3), (200, 2, 4)] Any idea why zip(*L, K) fails? I believe the *'ed item needs to be the last argument. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] iterating through large dictionary
D:\Python24>ad-attr.py Traceback (most recent call last): File "D:\Python24\ad-attr.py", line 32, in ? for k, v in ad_dict(user): ValueError: too many values to unpack Try this instead ... I think it should help: for k,v in ad_dict(user).items(): in 2.3 and newer, the preferred function is 'iteritems()' instead of 'items()'. Faster, less mem use, etc. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Apology
gerardo arnaez wrote: I apologize to the group for the dupes and not cutting the extended tail of my previous messages apology accepted. Your penance is to rewrite one of your python programs in Perl. (-: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] What does Python gain by having immutable types?
Tony C wrote: The list variable is the same object, and contains the sorted list, so why bother with the complexity of immutable types at all? * only immutable objects can be dictionary keys * specifically immutable strings are a performance optimization ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] List comprehensions
Liam Clarke wrote: Is there any guides to this (possibly obtuse) tool? Think of it this way. A list comprehension generates a new list. So, you should think about list comps whenever you have old_list -> new_list style behavior. There are two advantages to list comps over map: 1) a list comp can use a predicate to filter results [ x for x in mylist if is Prime(x) ] for instance. that would be map(lambda x: x, filter(isPrime, mylist)) which is a little more dense. 2) usually there is no need for a lambda. Not that there is anything wrong with lambdas mind you (-: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unique elements mapping
Srinivas Iyyer wrote:
Hi all:
I have a question and I request groups help please.
My list has two columns:
NameState
DrewVirginia
NoelMaryland
NikiVirginia
Adams Maryland
JoseFlorida
Monica Virginia
Andrews Maryland
I would like to have my ouput like this:
Virginia : Drew,Niki,Monica
Maryland: Noel,Adams, Andrews
Florida: Jose
Can you help how should I code :
for line in my_list:
key = line.split('\t')[0]
val = line.split('\t')[1]
dict = dict(zip(key,val))
this was my strategy ... but I could not make it
work..
You have the right idea. Just bad implementation (-:
uniques = {} # never name them 'dict', that is a type name in python
for line in my_list:
key, val = line.split('\t')
uniques.setdefault(val, []).append(key)
# in Python 2.4 the following two lines can be shortened to
# sorted_keys = sorted(unique.keys())
sorted_keys = unique.keys()
sorted_keys.sort()
for item in sort_keys:
print "%s: %s" % (item, ",".join(unique[item]))
So what we are doing is making a dict for which each element is a list
of names. The setdefault trick above is a neater way of saying:
if not uniques.has_key(val):
uniques[val] = []
uniques[val].append(key)
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Re: [Tutor] a shorter way to write this
jrlen balane wrote: basically, i'm going to create a list with 96 members but with only one value: list1[1,1,1,1...,1] is there a shorter way to write this one??? def generateN(n): while 1: yield n I'll leave the actual list creation up to you (-: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] a shorter way to write this
Smith, Jeff wrote: For all the talk of Python only having one way to do something which is why it's so much better than Perl, I've counted about 10 ways to do this :-) Knowing you said this at least half in jest, I still feel the need to comment. In any programming language, you have flexibility in how to define an algorithm. Think about how many different ways you can ask "is this string a in that string b?". The Python motto is actually better stated: there is one obvious way and it is often the right one. In the Python 1.5 days, choices were much fewer. With the new versions have come a more rich selection of features. Python's "only one way" is often brought up as a counterpoint to Perls TIMTOWTDI. Remembering which Perl idiom is the right one, for the right situation *AND* matches the rest of the project can be a real nightmare. Not to mention that choosing the wrong one often kills your performance (-: This is a big reason why I stick to Python. We may have choices, but they are often clear and obvious once you know the language. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Dates and databases, and blobs and Python.
Liam Clarke wrote:
And then there's the overall question -
What would be the least fiddly & least error prone way of working with
dates and times? Python or SQL?
Liam, SQL is another language. You need to learn it like you are
learning Python. It has pretty decent support for dates and times as
part of the ANSI SQL spec.
There are defined types, SQL functions, etc.
week(date) = week(mydate) for instance.
I tend to prefer to write programming language agnostic databases
because that way I can interact with them from any random language I
need to. Sometimes things go bad and a quick little script which does:
rows = exec("select * from table")
exec("begin transaction")
for row in rows:
row[3] = row[2] + row[4] - 5 # we decided on a new value
exec("update fields in table")
can be handy.
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Re: [Tutor] primes - sieve of odds
John Miller wrote: How does one actually use this module? For example: >>> import eratosthenes >>> eratosthenes.primes() >>> eratosthenes.primes().next() 2 >>> eratosthenes.primes().next() 2 >>> eratosthenes.primes().next() 2 How does one get beyond the first prime? it = eratosthenes.primes() it.next() it.next() or # 'it' is shorthand for iterator def primesToN(n): it = eratosthenes.primes() return [ x for x in it if x <= n ] You were running into problems because the primes() function returns a new generator. The values are in the generator not the function primes(). ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How and where to use pass and continue
Kevin wrote: I am having lot of trouble learning where and when to use pass and continue. The two books that I use don't explian these very good. Is there a website the explains these is great detail? I have also looked at the python tutorial as well. language idioms are one of the hardest things to learn and only really come after having written code and then coming back to it later. My thoughts on the subject. continue is a common idiom in I/O routines. for line in fp.xreadlines(): line = line.strip() if not line: continue # process line data here pass is an odd one. I tend to use it while prototyping to set up the bones of control statements to be. def func(one, two): if sometest(one): pass # need to actually do something here # work with one and two pass can also be used in multi-catch functions / control statements if input == 'something': handle_something(input) elif input == 'other': pass else: # do stuff here We want to ignore 'other' for some reason, so just use pass. Also handy if a value could be one of N choices but we only handle a few cases. This way someone else reading the code does not think "hey wait, they do not check for 'foo'!". ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How and where to use pass and continue
Kevin wrote:
Ok I have another question now I noticed that at the tope of a while
loop there will be somthing like this:
test = None
while test != "enter":
test = raw_input("Type a word: ")
if test == "enter":
break
what is the purpose of test = None ?
'test' must be given a value before Python will use it.
Without the first assignment, the program will fail to execute the first
time it reaches the unknown variable.
Think of it as riming the pump.
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Re: [Tutor] If elif not working in comparison
gerardo arnaez wrote: On Mon, 28 Mar 2005 09:27:11 -0500, orbitz <[EMAIL PROTECTED]> wrote: Floats are inherintly inprecise. So if thigns arn't working like you expect don't be surprised if 0.15, 0.12, and 0.1 are closer to the same number than you think. Are you telling me that I cant expect 2 digit preceision? Not without using round. Have *NO* faith in floating points. This is especially true when you are creating the decimals via division and the like. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] If elif not working in comparison
Kent Johnson wrote: Not without using round. Have *NO* faith in floating points. This is especially true when you are creating the decimals via division and the like. What?!?! OK, floats don't necessarily have the exact values you expect (they may have errors after many decimal places), and comparing floats for equality is risky business (you should compare for close, not equal). But the errors are well past the two-digit place. See the FAQ for more info on one kind of error: http://www.python.org/doc/faq/general.html#why-are-floating-point-calculations-so-inaccurate Note that the original poster was looking at ranges, not looking for exact matches! Can you be more specific about what kinds of problems you have had? sure, what is 2/3? 0.66? 0.67? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] If elif not working in comparison
Smith, Jeff wrote: Which is just what you'd expect. It's absolutey absurd to tell someone to have *NO* faith in floating numbers. It's like anything else in programming: you have to understand what you are doing. Unless a float that has been through a round function I do not trus it. That is what I mean by no faith. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Class and methods?
Kevin wrote: In a class is every def called a method and the def __init__(self) is called the constructor method? This class stuff is a little confusing. I don't have a problem writting a def I am still not clear on how to use a constructor. Is there a site that explains the constructor in great detail? a method is simply a function attached to an object which acts on that object. Nothing fancy. You can think of __init__ as a constructor. I have seen Python people refer to it as an initializer as well. All __init__ is doing is preparing the object for use. Give initial values to any variables, setup any datastructures, and/or maybe call a few other functions / classes. thing = MyClass(a,b) the call to MyClass above gets mapped to MyClass.__init__(a,b). Logically the flow is: Python makes an instance of the object (MyClass) Python calls __init__ if it is defined when __init__ returns Python assigns the object to the waiting variable ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] I am puzzled - help needed
John Carmona wrote: I am not sure that it is possible to ask that question please feel free to turn me down if it is going against the forum rules. I have going through Josh Cogliati tutorial, I am stuck on one of the exercise. I need to rewrite the high_low.py program (see below) to use the last two digits of time at that moment to be the "random number". This is using the import time module. I just can't work out how to do that, I have been looking at it for the past 2,5 hours but can't break it. Has anyone done it in order for me to study it. Many thanks in advance for any help It helps to know what you are having prolems with. Can you not get the time from the time module? Is getting the last two digits causing you fits? We do not mind helping people learn or even do their homework. We just don't like to give out the answers (-: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] sorting a list of dictionaries
Gooch, John wrote:
I am working on a dictionary sorting problem just like the one in the email
thread at the bottom of this message. My question about their solution is:
In these lines:
lst.sort(lambda m, n: cmp(m.get(field), n.get(field)))
where field is either 'name' or 'size'.
What is "n:" and what is "lambda m" ?
#!/usr/bin/python
lst = [{"foo": 6, "bar": 10}, {"foo": 1, "bar": 2}]
field = "foo"
sort_func = lambda m, n: cmp(m.get(field), n.get(field))
lst.sort(sort_func)
print sort_func(lst[0], lst[1])
print lst
lambda creates a nameless function.
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Re: [Tutor] Has anyone ever tried to convert the textual output of the dis module to another language
R. Alan Monroe wrote: Just curious. Googling for 'python "dis module" convert "another language" ' only got two hits. So maybe no one is trying it? I was just daydreaming about a native python compiler, and wondered how feasible it would be. There is already a python -> exe converter. Comes up on the list now and then. What would your idea change? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Has anyone ever tried to convert the textual output of the dis module to another language
R. Alan Monroe wrote: The main things about it that would make it appealing to me: #1 - MUCH MUCH MUCH smaller exes. Speed is not an issue to me, but filesize is. Have you ever compiled "Hello world" in a new language, and found that the exe was 100K+, when it really only needs to be less than 1K? And py2exe... I am not averse to using it, but 800 - 1000K+ exes, well, it's just my pet peeve. #2 - Love of classic hacking wizardry. :^) The problem is Python is a dynamic language so you HAVE to ship a runtime with it. That hello world bin may be small, but you will still have the Python runtime (at least a meg or so). Consider also module imports. Do they get compiled into the program? Shipped as a dynamic linked library? Personally, it sounds like a nifty learning project. Realistically that seems to be the only benefit. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] OT self-implementation?
Brian van den Broek wrote: > Now's not the time in my life to start a comp. sci. degree. So, my > questions are: > > 1) What would be good terms to google for to find an explanation of > how the seeming magic doesn't violate all reason? > > 2) Much harder, so please pass unless you've a link you know of > off-hand: any recommendations of particular things that I could read? > try a book on compiler design. If you have programmed for any length of time, the ideas will be easy enough to follow even if you do not follow the data structures and algorithms side. As for the lisp people, they insist everyone has been reimplementing lisp - badly. That is the advantage of being one of the first languages. To directly answer them, the lisp language was originally a mathematics theory. It was not meant to be run, you were supposed to apply logic to the thing. Then someone noticed that if you ran (eval myprog) suddenly your script could execute itself and the interpreter was born. How do you build tools without tools? That is the basis of your question. Ponder that. If you wanted to start your own blacksmith shop a thousand years or so ago, how would you do it? How do you make a framing square actually be square without using another square? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] dictionary
Shi Mu wrote:
> I typed:
> landUse = {'res': 1, 'com': 2, 'ind': 3, "other" :[4,5,6,7]}
> and when i checked landUse, I found it become:
> {'ind': 3, 'res': 1, 'other': [4, 5, 6, 7], 'com': 2}
> why the order is changed?
the docs warn you about this.
A dictionary stores its values based on the keys. Internally Python
sorts the keys to make the lookup meet performance expectations.
You can not expect a dictionary to return keys in the other you added
them. If you want that, store the items as tuples in a list.
landUse = [('res', 1), ('com', 2), ('ind', 3), ("other", [4,5,6,7])]
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Re: [Tutor] Percentage
Johan Geldenhuys wrote: > Hi all, > > What is the syntax if I want to work out what percentage 42 is out of 250? > 42 is x percent of 250. (is / of) = (x / 100) one of those formulas from school I will always remember. (42 / 250) = (x / 100.0) 250x = 4200.0 x = 4200.0 / 250 x = 16.8% ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] lunch.py
Christopher Spears wrote:
> I'm working on a program where a Customer orders Food
> from an Employee. Here is what I have so far:
>
> class Food:
> def __init__(self, name):
> Food.foodName = name
>
what you want here is 'self.name = name' then in your code later you can do:
protein = Food("hamburger")
lipid = Food("olive oil")
print protein.name
print lipid.name
> class Customer:
> def __init__(self,name):
> Customer.name = name
> def placeOrder(self, employee, food):
> print "%s, I want, %s please! " % Employee.name,
> food.foodName
>
> class Employee:
> def __init__(self, name):
> Employee.name = name
>
same for these, use self.name.
'self' is the item you are constructing. in my example above the Food
class is instantiated with the name 'hamburger' and assigned to protein.
When your code assigned to Food.foodName you were making *ALL* instances
of Food be the same food. Observe:
>>> class Food:
... def __init__(self, name):
... Food.foodName = name
...
>>> protein = Food('hamburger')
>>> protein.foodName
'hamburger'
>>> lipid = Food('olive oil')
>>> lipid.foodName
'olive oil'
>>> protein.foodName
'olive oil'
So to recap, use the class name when you want all instances to share a
variable i.e. a count of the number of items. Use 'self' when you want
each instance to have its own version of the variable, like your 'name'.
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Re: [Tutor] Why None?
Hey Chris, check out this version.
class Food:
def __init__(self, name):
self.name = name
class Customer:
def __init__(self,name):
self.name = name
self.food = None # 0 is for numbers
def placeOrder(self, foodName, employee):
print "%s: Hi %s!" % (self.name, employee.name)
print "%s: I want %s please! " % (self.name, foodName)
self.food = employee.takeOrder(foodName)
def foodOrdered(self):
return self.food.name
class Employee:
def __init__(self, name):
self.name = name
def takeOrder(self, foodName):
print "%s: %s coming up!" % (self.name, foodName)
return Food(foodName)
class MealOrder:
def __init__(self, employee, customer):
self.employee = employee
self.customer = customer
def set(self, foodName):
self.customer.placeOrder(foodName, self.employee)
def result(self):
print "%s has %s" % (self.customer.name,
self.customer.foodOrdered())
if __name__ == '__main__':
order = MealOrder(Employee('Dave'), Customer('Chris'))
order.set('spam')
order.result()
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Re: [Tutor] Does casting exist in Python?
Edgar Antonio Rodriguez Velazco wrote: > Does it? > Thanks, > not exactly. new_list = list(my_tuple) In general Python works without having to nudge the type system. For char -> int style conversions there is a builtin function called 'ord'. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Repeating a routine
Jumping to the middle of a book or movie will lead to similar confusion. Give a look at Dive Into Python. Available as either a book or online. http://www.diveintopython.org/ ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] list packing
John Fouhy wrote:
> On 27/02/06, kevin parks <[EMAIL PROTECTED]> wrote:
>
>>snd = [f for f in os.listdir('/Users/kevin/snd/') if f.endswith('.aif')]
>
>
> If this is all you need, then you could do something like:
>
> snd = ['/Users/kevin/snd/%s' % f for f in
> os.listdir('/Users/kevin/snd/') if f.endswith('.aif')]
>
> Or, slightly more robustly (?),
>
> snd = [os.path.join('/Users/kevin/snd', f) for f in
> os.listdir('/Users/kevin/snd/') if f.endswith('.aif')]
>
os.path.join() is self-documenting. I find this to be a better reason to
use it than anything else. But then my code only ever runs on Unix of
some flavor.
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Re: [Tutor] Python challenge
David Holland wrote: > I looked at this and got stuck on the first one :- Thanks for this. I missed it the first time it showed up on this list. Kinda fun and reminds me why I love python. Four lines in the interactive interpreter and most of the challenges are solved. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] understanding __import__()
Ok, this may be slightly above tutor's level, but hey, never hurts to ask (-: I am playing with __import__(). Here is my code: [code] import os.path app_path = '/tmp/my/settings' app_path2 = 'my/settings' if os.path.exists(app_path + '.py'): print "Found", app_path try: f = __import__(app_path, globals(), locals(), []) print f.__name__, f.__file__ except Exception, e: print e if os.path.exists(app_path2 + '.py'): print "Found", app_path2 try: f = __import__(app_path2, globals(), locals(), []) print f.__name__, f.__file__ except Exception, e: print e [/code] The result is the first import fails and the second one works. Even though they are the same file. $ pwd /tmp $ ls importer.py my/ $ ls my settings.py $ ./importer.py Found /tmp/my/settings No module named /tmp/my/settings Found my/settings my/settings /tmp/my/settings.py What gives?? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] understanding __import__()
Kent Johnson wrote: > The first argument to __import__ should be a module or package name, not > a file path, e.g. "my.settings". Python will look for the module in the > current sys.path the same as if you used a normal import. Apparently the > / is being interpreted as a . and I guess you have a file my/__init__.py so > import my.settings > will work but > import .tmp.my.settings > doesn't. > as I mention in another email, if I do: import sys sys.path.insert(0, '') It all just works. Very confused. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Python decorator
János Juhász wrote:
> Hi,
>
> I have just started to play with TurboGears - it is really nice - and I
> couldn't understand the decorators used by it.
> I have tried to interpret the http://wiki.python.org/moin/PythonDecorators
> about decorators, but it is too difficult for me.
>
> May someone explain decorators in very sortly, what is it for and why ?
> Do I need it anyway ?
>
A decorator is a function that takes a function and returns a new,
modified function.
In Django (a similar framework) there are a few places where decorators
are used.
@login_required
def foo_view(args):
# a view that must be authenticated
# more code here
This means that before foo_view() is ran the function login_required is
run. Which in this case will redirect to a login screen if the user is
not currently authenticated.
here's the Django code:
def user_passes_test(test_func, login_url=LOGIN_URL):
"""
Decorator for views that checks that the user passes the given test,
redirecting to the log-in page if necessary. The test should be a
callable
that takes the user object and returns True if the user passes.
"""
def _dec(view_func):
def _checklogin(request, *args, **kwargs):
if test_func(request.user):
return view_func(request, *args, **kwargs)
return HttpResponseRedirect('%s?%s=%s' % (login_url,
REDIRECT_FIELD_
NAME, quote(request.get_full_path(
_checklogin.__doc__ = view_func.__doc__
_checklogin.__dict__ = view_func.__dict__
return _checklogin
return _dec
login_required = user_passes_test(lambda u: u.is_authenticated())
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