Re: [Tutor] __init__() - is it required?
"bob gailer" wrote No, init() is only for initialising the object instance. If you have no local instance spwecific initialisation you can leave it to the inherited init() aor have no init() at all. Well I'd like to expand that a bit. There are cases where I create a class attribute and update it each time an instance is created. O Good point. init() can legitimately do things other than initialising instance variables, but conceptually those things are all part of initialising an instance. Updating class variables is a good example of such "other things". Alan G. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Try except really better than if?
Thank you Steven, Modulok and Alan for your precious and detailed explanations! I understood that I must not overuse try-except statement and usually when the exception could happen exceptionally. By the way I have this piece of code using elementTree standard module and according to Alan this is bad code I guess: *try: devdb.setDescription(dev.attrib['description']) except KeyError: pass try: devdb.setSymbolName(dev.attrib['symbolName']) except KeyError: pass try: devdb.setSymbolPinOrderMappingList(dev.attrib['symbolPinOrderMappingList']) except KeyError: pass try: devdb.setLayoutName(dev.attrib['layoutName']) except KeyError: pass try: devdb.setLayoutType(dev.attrib['layoutType']) except KeyError: pass * In fact elementTree *attrib* dictionary attributes could not have optionally xml attribute (depending on my xml input file). Indeed to test existence I try to execute *dev.attrib['//'*]. But I can't use only one except because the other settings could not be processed if one given optional xml attribute is not present (except will be raised). I must did it for each possible attribute. Do you have an alternative or my way is ok? I know there is no special case which is enough special to break the rule ;o) Regards Karim On 01/10/2011 03:10 AM, Alan Gauld wrote: ctions are slower than static functions, but that ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Checkbox problem in Tkinter
"ANKUR AGGARWAL" wrote from Tkinter import * root=Tk() var=StringVar() c=Checkbutton(root,text="hello",variable=var,onvalue="",offvalue="") c.pack() root.mainloop() FWIW I get a different problem, namely that the var does not seem to get updated nor does changling the var seem to alter the buuttons state. But at least the button displays OK with 'hello' in the label and I can select/deselect it with the mouse. its just the change to the variable that is broken. If I write an explicit event handler: def f(): var = '' if var == '' else '' Then var changes OK. Here is my code(from Pythonwin): def f(): global var; var = 'on' if var == 'off' else 'off';print var ... top = Tk() var = StringVar() c = Checkbutton(top,text='txt', variable=var, onvalue='on', offvalue='off', command=f) c.pack() top.mainloop() off on off on off on HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Try except really better than if?
By the way I have this piece of code using elementTree standard module >and according to Alan this is bad code I guess: > > Which just proves there are no absolute rules in programming :-) try: devdb.setDescription(dev.attrib['description']) >except KeyError: pass >try: devdb.setSymbolName(dev.attrib['symbolName']) >except KeyError: pass >try: devdb.setSymbolPinOrderMappingList(dev.attrib['symbolPinOrderMappingList']) >except KeyError: pass >try: devdb.setLayoutName(dev.attrib['layoutName']) >except KeyError: pass >try: devdb.setLayoutType(dev.attrib['layoutType']) >except KeyError: pass >Since you just use pass to ignore the error then you are kind of forced to do it this way. Its not bad each statement has to be treated individually, it is not a block where all the statements must pass or fail as a unit. > Do you have an alternative or my way is ok? This would also be a valid case for an if/else check but in readability terms I think try/except still wins because the handler is only a pass. If it were more complex I'd probably opt for if/else. I know there is no special case which is enough special to break the rule ;o) >I'm not sure I agree. In programming you can usually find a special case that validly breaks any "rule"! Even "Don't use goto!" :-) HTH, Alan G.___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Try except really better than if?
Thanks Alan this reassures me! Regards Karim On 01/10/2011 10:39 AM, ALAN GAULD wrote: By the way I have this piece of code using elementTree standard module and according to Alan this is bad code I guess: Which just proves there are no absolute rules in programming :-) *try: devdb.setDescription(dev.attrib['description']) except KeyError: pass try: devdb.setSymbolName(dev.attrib['symbolName']) except KeyError: pass try: devdb.setSymbolPinOrderMappingList(dev.attrib['symbolPinOrderMappingList']) except KeyError: pass try: devdb.setLayoutName(dev.attrib['layoutName']) except KeyError: pass try: devdb.setLayoutType(dev.attrib['layoutType']) except KeyError: pass * Since you just use pass to ignore the error then you are kind of forced to do it this way. Its not bad each statement has to be treated individually, it is not a block where all the statements must pass or fail as a unit. > Do you have an alternative or my way is ok? This would also be a valid case for an if/else check but in readability terms I think try/except still wins because the handler is only a pass. If it were more complex I'd probably opt for if/else. I know there is no special case which is enough special to break the rule ;o) I'm not sure I agree. In programming you can usually find a special case that validly breaks any "rule"! Even "Don't use goto!" :-) HTH, Alan G. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Try except really better than if?
Karim wrote:
Thank you Steven, Modulok and Alan for your precious and detailed
explanations!
I understood that I must not overuse try-except statement and usually
when the exception could happen exceptionally.
By the way I have this piece of code using elementTree standard module
and according to Alan this is bad code I guess:
*try: devdb.setDescription(dev.attrib['description'])
except KeyError: pass
[...]
Whenever you have very similar code repeated many times, you should
consider factoring out the common code into a helper function. Something
like this:
def try_or_pass(key):
attr_name = 'set' + key[0].upper() + key[1:]
try:
getattr(devb, attr_name)(dev.attrib[key])
except KeyError:
pass
try_or_pass('description')
try_or_pass('symbolName')
etc.
--
Steven
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Re: [Tutor] Try except really better than if?
Steven many thanks for this useful hint!
I will modify my code.
Many thanks!
Regards
Karim
On 01/10/2011 11:32 AM, Steven D'Aprano wrote:
Karim wrote:
Thank you Steven, Modulok and Alan for your precious and detailed
explanations!
I understood that I must not overuse try-except statement and usually
when the exception could happen exceptionally.
By the way I have this piece of code using elementTree standard
module and according to Alan this is bad code I guess:
*try: devdb.setDescription(dev.attrib['description'])
except KeyError: pass
[...]
Whenever you have very similar code repeated many times, you should
consider factoring out the common code into a helper function.
Something like this:
def try_or_pass(key):
attr_name = 'set' + key[0].upper() + key[1:]
try:
getattr(devb, attr_name)(dev.attrib[key])
except KeyError:
pass
try_or_pass('description')
try_or_pass('symbolName')
etc.
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Re: [Tutor] Try except really better than if?
Alan Gauld wrote: However, using exceptions like if/else blocks is bad practice. I'm afraid I disagree strongly with that! You need to use them like a commit in SQL - to protect a whole block of code. Putting try/except around every line of code defeats the purpose, wrap atomic blocks of code not the individual lines. Wrapping an atomic block of code, so long as it actually *can* be treated as atomic (including backing out any changes if it fails), is a good use of try...except. But otherwise, this is risky advice. Take your example: try: something something else another the last except Error1: # do something except Error2: # do something except Error3: # do something finally: # tidy up Provided the entire try block needs to be treated as a single operation (in which case, why isn't it a function?) then that's not too bad. But the risk comes from people who wrap large blocks of code *without* making them atomic transactions: try: get_job_id() query_database() send_results() push_ticket() update_counter() except KeyError: print "job failed" And now an error in push_ticket means that the counter fails to be updated even though the results were sent. Problems occur. The try block must contain ONE operation. It doesn't matter if the operation is a simple, atomic operation: try: y = x + 1 except... or a large, complex transaction, so long as it can safely be treated as a single operation. That is, the individual sub-tasks should have no side-effects, or they must be backed out off on failure. The other problem is that large try blocks can mask bugs. Here's my example again: try: get_job_id() query_database() send_results() push_ticket() update_counter() except KeyError: print "job failed" The idea being that get_job_id or query_database might raise KeyError. But update_counter should never raise KeyError. If it does, that indicates a bug in update_counter, which will then be masked by the except as a normal error in processing. This would be better: try: get_job_id() query_database() except KeyError: print "job failed" else: send_results() push_ticket() update_counter() Now the else block is only executed if there is no KeyError, and any exceptions in those three will be detected and not masked. Of course, you can then wrap the entire code block in another try...except, try...else or try...finally block. Something like this perhaps? try: try: get_job_id() query_database() except KeyError: print "job failed" else: # no exception caught send_results() push_ticket() update_counter() failed = True finally: if transaction_succeeded(): commit_transaction() else: rollback() And now you are beginning to see why databases are so complicated. is better to maintain than try: something except Error1: # do something try: something else except Error2: # do something try: another except Error1: # and again try: the last except Error3: do it tidy up That's what you have to do if something, something else, etc. need to be treated as independent operations that have to be done regardless of the success or failure of those that come before. Otherwise: try: something try: something_else try: another except Error1: ... except Error2: ... except Error1: ... It has been said that error handling is ten times harder than handling the rest of your code. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Checkbox problem in Tkinter
ANKUR AGGARWAL wrote:
> and i got the output as -
> [image: Screenshot.png]
The image doesn't survive.
> When i take the var as of string variable type i am unable to edit the
> checkbox. It comes slected predefined and the widget in kindof Invisible
> and
> u can say uneditable. Can anybody tell me whats i am doing wrong in
> this??? Its works fine if i take the var variable as the integer variable.
> I can deselect and select in that case and it gives me the desired result
> but in string case i am unable to do so as checkbox is invisible type.
> I am using Python 2.6
I can't reproduce that behaviour. The widget appears greyed initially, but
is still editible. You could try to initialise the StringVar with onvalue or
offvalue:
> from Tkinter import *
> root=Tk()
> var=StringVar()
var.set("")
> c=Checkbutton(root,text="hello",variable=var,onvalue="",
> offvalue="")
> c.pack()
> root.mainloop()
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Re: [Tutor] Checkbox problem in Tkinter
Alan Gauld wrote:
>
> "ANKUR AGGARWAL" wrote
>
>> from Tkinter import *
>> root=Tk()
>> var=StringVar()
>>
c=Checkbutton(root,text="hello",variable=var,onvalue="",offvalue="")
>> c.pack()
>> root.mainloop()
>
> FWIW I get a different problem, namely that the var does not seem
> to get updated nor does changling the var seem to alter the buuttons
> state. But at least the button displays OK with 'hello' in the label
> and
> I can select/deselect it with the mouse. its just the change to the
> variable that is broken.
> If I write an explicit event handler:
>
> def f():
> var = '' if var == '' else ''
>
> Then var changes OK. Here is my code(from Pythonwin):
>
def f(): global var; var = 'on' if var == 'off' else 'off';print
var
> ...
top = Tk()
var = StringVar()
c = Checkbutton(top,text='txt', variable=var, onvalue='on',
offvalue='off', command=f)
c.pack()
top.mainloop()
> off
> on
> off
> on
> off
> on
I think that is confusing. Tkinter is not supposed to rebind the global name
'var', it invokes its set() method. Try
from Tkinter import *
root = Tk()
var = StringVar()
def command():
print var.get()
cb = Checkbutton(root, text="yadda", onvalue="on", offvalue="off",
variable=var, command=command)
cb.pack()
root.mainloop()
You can also monitor changes to var's value directly:
from Tkinter import *
root = Tk()
var = StringVar()
def show(*args):
print var.get()
var.trace_variable('w', show)
cb = Checkbutton(root, text="yadda", onvalue="on", offvalue="off",
variable=var)
cb.pack()
root.mainloop()
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Re: [Tutor] Checkbox problem in Tkinter
ANKUR AGGARWAL wrote: > Hey I write this code up > > from Tkinter import * > root=Tk() > var=StringVar() > c=Checkbutton(root,text="hello",variable=var,onvalue="",offvalue="") > c.pack() > root.mainloop() > > and i got the output as - > [image: Screenshot.png] > > When i take the var as of string variable type i am unable to edit the > checkbox. It comes slected predefined and the widget in kindof Invisible > and > u can say uneditable. Can anybody tell me whats i am doing wrong in > this??? Its works fine if i take the var variable as the integer variable. > I can deselect and select in that case and it gives me the desired result > but in string case i am unable to do so as checkbox is invisible type. > I am using Python 2.6 > Thanks In Advance > Ankur Aggarwal The variable appears greyed out because initially var.get() == "", see http://www.tcl.tk/man/tcl8.5/TkCmd/checkbutton.htm#M-tristatevalue ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] about import statement
Hi Friends, I'm Arun Kumar from India, Just a month ago i started learning programming .learned some basics of python. I'm really enjoying programming in python. I have some doubts in python. When we write programs,we write some import statements at the beginning of the code. how to know that we should import something. How do we know that certain classes are in particular module? Thanks Arun Kumar ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about import statement
On 1/10/2011 7:58 AM, arun kumar wrote: Hi Friends, I'm Arun Kumar from India, Just a month ago i started learning programming .learned some basics of python. I'm really enjoying programming in python. I have some doubts in python. When we write programs,we write some import statements at the beginning of the code. how to know that we should import something. How do we know that certain classes are in particular module? Python comes with basic functionality built-in. In addition there are many modules included in the Python distribution to supply additional functionality. See the Global Module Index in the Documentation. Unfortunately the list is large - and many of the modules are very specialized. I suggest reading (at minimum) the descriptions for collections, copy, decimal, exceptions, glob, itertools, math, operator, os, pickle (and shelve), re, shutil, sys, time. In addition there are many many other packages for extending Python that are not in the distribution that add more modules. You can also write your own modules. This is a way to - break a complex program into smaller pieces (that often can be independently tested) - create common code to be used by more than one main program. HTH. Please return with more questions. -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about import statement
On Jan 10, 2011, at 7:58 AM, arun kumar wrote: > how to know that we > should import something. How do we know that certain classes are in > particular module? You know to import a module if you need part of that module. Perhaps you need a class or function defined in the module. There are several ways to see what a module provides. The documentation is usually a good place to start. You can also use dir(), e.g. import foo; dir(foo). ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Equality of numbers and Strings
Hello All,
I am not a beginner in Python language but I discovered a hidden
property of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically).
I get the same object in py db. It could be evident but if I do the same
(same elements) with a list it
will not give the same result. Is-it because of immutable property of
strings and numbers?
Regards
Karim
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Re: [Tutor] Equality of numbers and Strings
On 1/10/2011 8:07 AM Karim said...
Hello All,
I am not a beginner in Python language but I discovered a hidden
property of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically).
well, not predictably unless you understand the specifics of the
implementation you're running under.
>>> from string import letters
>>> longstring = letters*100
>>> otherstring = letters*100
>>> id(longstring)
12491608
>>> id (otherstring)
12100288
>>> shortstring = letters[:]
>>> id(letters)
11573952
>>> id(shortstring)
11573952
>>>
I get the same object in py db. It could be evident but if I do the same
(same elements) with a list it
will not give the same result. Is-it because of immutable property of
strings and numbers?
It has to do with Interning -- see eg
http://docs.python.org/library/functions.html#intern
Generally, the shorter strings are interned to speed up dictionary
access. At this point, I'd characterize the coincidence of id()s as
more of an implementation detail side effect than anything else.
Emile
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Re: [Tutor] Equality of numbers and Strings
On 1/10/2011 11:07 AM, Karim wrote:
Hello All,
I am not a beginner in Python language but I discovered a hidden
property of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically).
Python "interns" certain literal strings - so a 2nd attempt to create
'xyz' will refer back to the original object.
I don't know all the rules - but the following program never prints n:
for n in range(1,1):
s = eval("'" + 'wrtnjasdflkasjj'*n + "'")
t = eval("'" + 'wrtnjasdflkasjj'*n + "'")
if id(s) != id(t):
print n; break
whereas if I insert a ";" in the literal the program prints 1!
Also note str() returns the argument object unchanged.
--
Bob Gailer
919-636-4239
Chapel Hill NC
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Re: [Tutor] about import statement
On 1/10/2011 4:58 AM arun kumar said... Hi Friends, I'm Arun Kumar from India, Just a month ago i started learning programming .learned some basics of python. I'm really enjoying programming in python. I have some doubts in python. When we write programs,we write some import statements at the beginning of the code. how to know that we should import something. How do we know that certain classes are in particular module? I found effbot's guide to the standard library helpful -- and although it's nor current, you'll still get a good idea of where things are at and how to use them. See http://effbot.org/zone/librarybook-index.htm Also, experiment with help() from the python prompt. Once in the help system, type in 'modules' to see a list of installed available modules to explore, or a module name for more info on that module. HTH, Emile ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Equality of numbers and Strings
On 1/10/2011 11:51 AM, Emile van Sebille wrote:
well, not predictably unless you understand the specifics of the
implementation you're running under.
>>> from string import letters
>>> longstring = letters*100
>>> otherstring = letters*100
>>> id(longstring)
12491608
>>> id (otherstring)
12100288
>>> shortstring = letters[:]
>>> id(letters)
11573952
>>> id(shortstring)
11573952
>>>
In my experiment I found that using * to replicate gave different
results than using the exact literal. That is why in the program I
posted I used the equivalent of eval("'" + letters*n + "'") which gives
different results than eval("letters*n")!
[snip]
--
Bob Gailer
919-636-4239
Chapel Hill NC
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Re: [Tutor] Equality of numbers and Strings
On Mon, Jan 10, 2011 at 8:54 AM, bob gailer wrote:
> On 1/10/2011 11:07 AM, Karim wrote:
>
>>
>> s ='xyz'
>> >>> t = str('xyz')
>>
>> >>> id(s) == id(t)
>> True
>>
>> Thus if I create 2 different instances of string if the string is
>> identical (numerically).
>>
>
> Python "interns" certain literal strings - so a 2nd attempt to create 'xyz'
> will refer back to the original object.
>
i haven't researched all the rules for strings either, but from my
understanding, they're short(er) strings which are used often enough to
warrant interning.
the (current) rule for ints is: range(-5, 257). i say current because before
2.5, it was range(-1, 101). no one bothered to tell me when i updated Core
Python to a 2nd ed. good thing i checked before it went to press! :P
note that floats are also immutable, but they're never interned, so you'll
never get the same one twice unless you're really referring to the same
object. same goes for complex, etc. interning is strictly for commonly-used
small ints and short strings.
cheers,
-- wesley
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"Core Python Programming", Prentice Hall, (c)2007,2001
"Python Fundamentals", Prentice Hall, (c)2009
http://corepython.com
wesley.j.chun :: wescpy-at-gmail.com
python training and technical consulting
cyberweb.consulting : silicon valley, ca
http://cyberwebconsulting.com
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Re: [Tutor] Equality of numbers and Strings
On 1/10/2011 9:23 AM bob gailer said...
On 1/10/2011 11:51 AM, Emile van Sebille wrote:
well, not predictably unless you understand the specifics of the
implementation you're running under.
>>> from string import letters
>>> longstring = letters*100
>>> otherstring = letters*100
>>> id(longstring)
12491608
>>> id (otherstring)
12100288
>>> shortstring = letters[:]
>>> id(letters)
11573952
>>> id(shortstring)
11573952
>>>
In my experiment I found that using * to replicate gave different
results than using the exact literal. That is why in the program I
posted I used the equivalent of eval("'" + letters*n + "'") which gives
different results than eval("letters*n")!
[snip]
Hence, not predictably.
I also found it particularly interesting that an explicit copy didn't:
shortstring = letters[:]
Emile
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Re: [Tutor] Equality of numbers and Strings
Emile van Sebille, 10.01.2011 18:42:
On 1/10/2011 9:23 AM bob gailer said...
On 1/10/2011 11:51 AM, Emile van Sebille wrote:
well, not predictably unless you understand the specifics of the
implementation you're running under.
>>> from string import letters
>>> longstring = letters*100
>>> otherstring = letters*100
>>> id(longstring)
12491608
>>> id (otherstring)
12100288
>>> shortstring = letters[:]
>>> id(letters)
11573952
>>> id(shortstring)
11573952
>>>
In my experiment I found that using * to replicate gave different
results than using the exact literal. That is why in the program I
posted I used the equivalent of eval("'" + letters*n + "'") which gives
different results than eval("letters*n")!
Hence, not predictably.
I also found it particularly interesting that an explicit copy didn't:
shortstring = letters[:]
There's no need to copy an immutable object.
Stefan
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Re: [Tutor] Equality of numbers and Strings
Karim, 10.01.2011 17:07:
I am not a beginner in Python language but I discovered a hidden property
of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically). I get the same object in py db. It could be
evident but if I do the same (same elements) with a list it will not
give the same result. Is-it because of immutable property of strings and
numbers?
AFAIR, all string literals in a module are interned by the CPython
compiler, and short strings that look like identifiers are also interned
(to speed up dictionary lookups, e.g. for function names). So you will get
identical objects in these cases, although it's not a good idea to rely on
this as it's an implementation detail of the runtime.
And the second thing that you can observe here is that str() never copies a
string you pass in, which is reasonable behaviour for immutable objects.
Thus if I create 2 different instances of string if the string is
identical (numerically).
There's no such thing as "numerically identical" strings. It's enough to
say that they are identical as opposed to equal.
Stefan
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Re: [Tutor] Try except really better than if?
"Steven D'Aprano" wrote Wrapping an atomic block of code, so long as it actually *can* be treated as atomic (including backing out any changes if it fails), is a good use of try...except. That's exactly what I meant by atomic. A (smallish) group of instructions that must be treated as a group, if any one fails the whole block fails and must be backed out or aborted. Provided the entire try block needs to be treated as a single operation (in which case, why isn't it a function?) The point about the function is good and the try/except can live within the function. a single operation. That is, the individual sub-tasks should have no side-effects, or they must be backed out off on failure. Absolutely. That is the key criterion. It has been said that error handling is ten times harder than handling the rest of your code. Yep, and usually takes up about ten times as much code. I once analyzed a largish project - about 1.5 million lines of C++. Only ~250k lines were actual funcionality, the rest were split between GUI (before GUI Builders etc) and error handling (and some logging for our IT department's benefit). I can't recall the split between GUI and errors but it was scary to see how little was real functonal code... ( This didn't include any SQL or script files but it was before the days of stored procedures so most of the SQL was probably ermbedded in the C++ anyway). HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Checkbox problem in Tkinter
"Peter Otten" <__pete...@web.de> wrote I can select/deselect it with the mouse. its just the change to the variable that is broken. This was the problem using the Stringvar. Then var changes OK. Here is my code(from Pythonwin): def f(): global var; var = 'on' if var == 'off' else 'off';print var ... top = Tk() var = StringVar() c = Checkbutton(top,text='txt', variable=var, onvalue='on', offvalue='off', command=f) c.pack() top.mainloop() off on I think that is confusing. Tkinter is not supposed to rebind the global name 'var', it invokes its set() method. Try Yes, my bad, I should have removed the StringVar assigment it was just a carryover from the previous attempt. The problem was that the StringVar was never changing when the control was clicked. This was my attempt to create a manual solution that avoided the automated StringVar approach. def command(): print var.get() This raises an interesting point though. I was printing var - which never changed - I forgot about the need to go through a get() method. Time for another experiment Alan G. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about import statement
"arun kumar" wrote I have some doubts in python. When we write programs,we write some import statements at the beginning of the code. how to know that we should import something. Trial and error, experience and mainly reading the documentation. You try to do something and there is no obvious direct solution in the basic Python built-in commands and functions, so we go to the module library to see if anything looks useful. Then we use dir() and help() to find out what is in the module and how to use it. If nothing exists in the library then we try Google and perhaps install a third party package. How do we know that certain classes are in particular module? dir(), help() and reading the documents. Sorry, there are no easier answers, but that kind of research is one of the keys to programming. And sometimes you will probably write code that could have been done via a module but you just didn't know it existed. I've done that lots of times! Reading this list is a good way to discover some of the more obscure but useful modules available. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Equality of numbers and Strings
Many thanks Emile, Bob, Stefan, Wesley!
Now, I see now that the point is more related to implementation details
and optimization instead of a true
property. But it could mistaken people not aware.
Regards
Karim
On 01/10/2011 06:56 PM, Stefan Behnel wrote:
Karim, 10.01.2011 17:07:
I am not a beginner in Python language but I discovered a hidden
property
of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically). I get the same object in py db. It could be
evident but if I do the same (same elements) with a list it will not
give the same result. Is-it because of immutable property of strings and
numbers?
AFAIR, all string literals in a module are interned by the CPython
compiler, and short strings that look like identifiers are also
interned (to speed up dictionary lookups, e.g. for function names). So
you will get identical objects in these cases, although it's not a
good idea to rely on this as it's an implementation detail of the
runtime.
And the second thing that you can observe here is that str() never
copies a string you pass in, which is reasonable behaviour for
immutable objects.
Thus if I create 2 different instances of string if the string is
identical (numerically).
There's no such thing as "numerically identical" strings. It's enough
to say that they are identical as opposed to equal.
Stefan
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Re: [Tutor] __init__() - is it required?
On 01/09/2011 04:27 PM, Steven D'Aprano wrote: > Corey Richardson wrote: >> Do all classes need an __init__() method? I have classes that look much >> like this one starts out: >> >> class GenerateXML(object): >> """Defines methods to be inherited for StaticXML and AnimationXML""" >> def __init__(self): >> pass >> >> I would rather not do that. Code without it runs fine, but will there be >> any negative consequences down the road? Does object define an __init__ >> method for me? > > You don't need to define an __init__ if you don't need one. A > placeholder __init__ that does nothing, as above, is a waste of space. > > object includes an __init__ method that not only does nothing, but > ignores any arguments you pass to it: > > >>> object.__init__ > > >>> object.__init__(1, 2, 3) > >>> > > In Python 2.x, you can have "old-style" classes that don't inherit from > object. They too don't need an __init__: > > >>> class Old: # *don't* inherit from object > ... pass > ... > >>> o = Old() > >>> > > Thank you very much Alan and Steven! ~Corey Richardson ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Missing Data in Txt Files
Hello, Does anyone have a program that will read txt file data and insert - or similar for missing data? I have 10minute data and there are hour chunks that are missing that need a missing data insert for that missing hour but not the 10min period. The txt file has a date column (yymmdd), a time (hhmm) column and the rest are data columns shown below. See column 1 below with i 080618 1000 4.62 7.00 227.0 -3.38 -3.15 0.00 .99 .99 0.91 080618 1410 5.19 7.30 232.0 -4.09 -3.20 0.00 .99 .99 1.03 Muchas gracias, Randall P. Benson, PhD Global Technical Division/Energy Resources O: 503-796-7129 M: 971-227-2477 -Original Message- From: tutor-bounces+randall.benson=iberdrolaren@python.org [mailto:tutor-bounces+randall.benson=iberdrolaren@python.org] On Behalf Of Corey Richardson Sent: Monday, January 10, 2011 1:25 PM To: tutor@python.org Subject: Re: [Tutor] __init__() - is it required? On 01/09/2011 04:27 PM, Steven D'Aprano wrote: > Corey Richardson wrote: >> Do all classes need an __init__() method? I have classes that look much >> like this one starts out: >> >> class GenerateXML(object): >> """Defines methods to be inherited for StaticXML and AnimationXML""" >> def __init__(self): >> pass >> >> I would rather not do that. Code without it runs fine, but will there be >> any negative consequences down the road? Does object define an __init__ >> method for me? > > You don't need to define an __init__ if you don't need one. A > placeholder __init__ that does nothing, as above, is a waste of space. > > object includes an __init__ method that not only does nothing, but > ignores any arguments you pass to it: > > >>> object.__init__ > > >>> object.__init__(1, 2, 3) > >>> > > In Python 2.x, you can have "old-style" classes that don't inherit from > object. They too don't need an __init__: > > >>> class Old: # *don't* inherit from object > ... pass > ... > >>> o = Old() > >>> > > Thank you very much Alan and Steven! ~Corey Richardson ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Please be advised that email addresses for Iberdrola Renewables personnel have changed to first.l...@iberdrolaren.com effective Aug. 16, 2010. Please make a note. Thank you. This message is intended for the exclusive attention of the recipient(s) indicated. Any information contained herein is strictly confidential and privileged. If you are not the intended recipient, please notify us by return e-mail and delete this message from your computer system. Any unauthorized use, reproduction, alteration, filing or sending of this message and/or any attached files may lead to legal action being taken against the party(ies) responsible for said unauthorized use. Any opinion expressed herein is solely that of the author(s) and does not necessarily represent the opinion of the Company. The sender does not guarantee the integrity, speed or safety of this message, and does not accept responsibility for any possible damage arising from the interception, incorporation of viruses, or any other damage as a result of manipulation. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Missing Data in Txt Files
On 1/10/2011 4:10 PM Benson, Randall said...
Hello,
Does anyone have a program that will read txt file data and insert -
or similar for missing data? I have 10minute data and there are hour
chunks that are missing that need a missing data insert for that missing
hour but not the 10min period. The txt file has a date column (yymmdd),
a time (hhmm) column and the rest are data columns shown below. See
column 1 below with i
080618 1000 4.62 7.00 227.0 -3.38 -3.15 0.00 .99 .99 0.91
080618 1410 5.19 7.30 232.0 -4.09 -3.20 0.00 .99 .99 1.03
Hi Randall,
First, please start a new thread next time -- you replied to an existing
thread which can cause your post to go unnoticed...
I doubt anyone will have a specific program to do what you're asking,
and for most of us writing this is what we'd expect to do.
I think I'd put the data into a dictionary and access the keys in a loop
with a default provided for missing keys. Something along the lines of:
lines = open('data/file/name').readlines()
D = dict((line{:11),line) for line in lines)
for timestamp in timestampgenerator:
data = D.get(timestamp,-)
...
Of course it all depends
Emile
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Re: [Tutor] Missing Data in Txt Files
"Benson, Randall" wrote hour but not the 10min period. The txt file has a date column (yymmdd), a time (hhmm) column and the rest are data columns shown below. See column 1 below with i Not sure what the last sentence merans? Was there supposed to be more? Or what is the 'i' referred to? 080618 1000 4.62 7.00 227.0 -3.38 -3.15 0.00 .99 .99 0.91 080618 1410 5.19 7.30 232.0 -4.09 -3.20 0.00 .99 .99 1.03 I'm not sure what this is telling me. Is there an example of such missing data here? Does 0.00 mean its missing? Or is it something else? What you want should be possible but we need a much clearer specification of the problem. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Missing Data in Txt Files
On 1/10/2011 7:10 PM, Benson, Randall wrote: Hello, Does anyone have a program that will read txt file data and insert - or similar for missing data? I have 10minute data and there are hour chunks that are missing that need a missing data insert for that missing hour but not the 10min period. The txt file has a date column (yymmdd), a time (hhmm) column and the rest are data columns shown below. See column 1 below with i 080618 1000 4.62 7.00 227.0 -3.38 -3.15 0.00 .99 .99 0.91 080618 1410 5.19 7.30 232.0 -4.09 -3.20 0.00 .99 .99 1.03 Muchas gracias, I agree with Alan. We need more detail. Why are you asking this question on the Python Tutor list? I presume you are using Python. We prefer to help you as you show us effort. Do you know enough Python to write a program that reads a file and creates another? I suggest you start with that, and also give us enough additional details so we fully understand what you want. Sample input - sample output would help a lot. -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
