Re: [Tutor] (no subject)
On 21/07/14 01:34, Marc Tompkins wrote: noticed that you often advise it. I don't know who _does_ think this is a desirable pattern; I'd love to hear their argument for it - it must be really good. Nope, it doesn't need to be "really good", it just needs to have enough advantage over the alternatives for people to prefer it. In the case of while loops the options are: 1) while True: while True: read input if end condition: break process loop 2) While test read input while test: process loop read input The argument against the latter form is simply that you have to maintain the read input line in two places. So far as I can tell, that's it. But it seems to be enough to make it the default Python while idiom. Now that doesn't mean that you should not use form 2 in Python, form 1 is only justified if you need to repeat the call (or the test). There are many cases where form 2 would be better,. and sadly sometimes we see form 1 being used when it should not. But even more often we see while loops being used where they should not. A for loop is usually a better option if the number of iterations is known. Loop choice is one area where Python is not as expressive as other languages but the two(*) we have are adequate if not ideal. (*)And you can extend those somewhat using generators and itertools. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Is this possible for a newbie?
Hi, Answers are below. - Original Message - From: keith papa Am a newbie to programming and I started learning python days ago. I have this idea I want to execute, am a big sport and fantasy fan and I wanted to create something that will make it things a little easy for me. My idea is simple I want to create a program that I can enter name and some information about a player, for example: NFL plays: Jamaal Charles RB : ATT 259 , YDS 1,287 , AVG 5.0, TD 12, REC 70 Tony Romo QB: CMP% 63.9, YDS 3,828 , TD 31, INT 10, Rating 96.7 Dez Bryant WR: REC 93, YDS 1,233, AVG 13.3, LNG 79, TD 13 and other players information. I want to be able to ask the program which QB is best on my list and it give me the names of all the QB on my list, or ask for WR on my list and it gives me all the WR on my list, and also I want to be able to crossed out name simply by typing the players name. What do I need to lean in order to accomplish this? string, variable functions? feel free to ask any questions. JL: I think learning about tuples and dictionaries might be your friends. There is a data type called tamed tuple that assigns names to fields, so you can ask your program to give you needed info by sorting by field names. Hope this helps. Cheers, Joseph attachment Description: Binary data ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (no subject)
Dear Gurus,
Thank-you thank-you, one more time, thank-you.
I am over that hurdle and have the other: converting the list of characters
that was just created by the split - into integers so I can manipulate them. I
was trying to convert to a string, then to integers. I have been scouring the
web for casting integers, converting to strings and also trying to look up the
error messages: I apologize for the mess - I was trying everything.
Sigh,
Python in the hands of the naïve
LN.
>>> numlist = data_value
>>> numlist
['36', '39', '39', '45', '61', '54', '61', '93', '62', '51', '47', '72', '54',
'36', '62', '50', '41', '41', '40', '62', '62', '58', '57', '54', '49', '43',
'47', '50', '45', '41', '54', '57', '57', '55', '62', '51', '34', '57', '55',
'63', '45', '45', '42', '44', '34', '53', '67', '58', '56', '43', '33']
>>> print sum(numlist)
Traceback (most recent call last):
File "", line 1, in
print sum(numlist)
TypeError: unsupported operand type(s) for +: 'int' and 'str'
>>> orange_drinkers = int(data_value)
Traceback (most recent call last):
File "", line 1, in
orange_drinkers = int(data_value)
TypeError: int() argument must be a string or a number, not 'list'
>>> int(data_value)
Traceback (most recent call last):
File "", line 1, in
int(data_value)
TypeError: int() argument must be a string or a number, not 'list'
>>> numstring = raw_input(">")
>
>>> type(numlist)
>>> b = str(numlist)
>>> c = []
>>> for digit in b:
c.append (int(digit))
Traceback (most recent call last):
File "", line 2, in
c.append (int(digit))
ValueError: invalid literal for int() with base 10: '['
>>> i = 0
>>> str(numlist)
"['36', '39', '39', '45', '61', '54', '61', '93', '62', '51', '47', '72', '54',
'36', '62', '50', '41', '41', '40', '62', '62', '58', '57', '54', '49', '43',
'47', '50', '45', '41', '54', '57', '57', '55', '62', '51', '34', '57', '55',
'63', '45', '45', '42', '44', '34', '53', '67', '58', '56', '43', '33']"
>>> int(x[,numlist])
SyntaxError: invalid syntax
>>> int(x[numlist])
Traceback (most recent call last):
File "", line 1, in
int(x[numlist])
TypeError: 'int' object has no attribute '__getitem__'
>>> for x in numlist:
i.append (int(x))
Traceback (most recent call last):
File "", line 2, in
i.append (int(x))
AttributeError: 'int' object has no attribute 'append'
>>>
On Sunday, July 20, 2014 6:21 PM, Wolfgang Maier
wrote:
On 20.07.2014 22:37, Marc Tompkins wrote:
>
> First of all, I would take advantage of the "with" construction, like so:
>
> with open('C:/Python27/egund919/Program1/BOJ_B.txt','r') as infile:
> #do stuff with infile
>
> When the block of code inside of the "with" section finishes, Python
> will take care of closing the file for you - even if your program
> encountered an error. MAJOR advantage over doing it yourself.
>
Yes, definitely, as you have experienced yourself now.
> Second, there's no need to import "string" anymore; all of the
> functions defined in that module are native methods of strings.
> "line" is a string, so you can just do "line.split()". split()
> returns a list; you can get the first item in that list with
> line.split()[0], the second item with line.split()[1], etc.
>
I fully agree on the string method part. As for the use of
line.split()[0] and [1], see my comment in the code below.
> Third, free your mind from the shackles of counting how many objects
> are in a list and using that counter as the index of your loops - this
> is not the Python way! Instead, let Python take care of the counting
> and indexing for you.
>
True (see the earlier suggestion of using enumerate()), but I'm sure
you'll learn this over time.
> Fourth (and here I differ from some of the others on this list,
> notably Alan G) - I don't like the "while True: / break" paradigm.
> Your mileage may vary, but I find it makes it harder to understand
> what the program is actually trying to achieve. In your case, you
> read a line from the file, then check whether it contains anything; I
> like to move the readline() to the bottom of the loop.
In my opinion, this is less readable than the original code. I know that
some people (usually coming from C or other languages with more
expressive while loops) don't like it, but there's nothing wrong, in
general, with using while True with break. It's perfectly pythonic.
Direct use of the file object in a for loop has been suggested already
and THAT's more readable.
>
> Having said all that, here's my suggested version:
>
> state_name = []
> data_value = []
> with open('C:/Python27/egund919/Program1/BOJ_B.txt','r') as infile:
> line = infile.readline() # Doing this twice because you
> apparently want to discard the first line...?
> line = infile.readline()
> while line:
> state_name.append(line.split()[0])
> data_value.append(line.split()[1])
Rewriting the original
States, OJ = string.split(line)
as
states
[Tutor] Unhandled exception
I just want to know if an unhandled exception is a bug in my programs! Degreat ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (no subject)
On 21.07.2014 01:48, LN A-go-go wrote:> Dear Gurus, > Thank-you thank-you, one more time, thank-you. > I am over that hurdle and have the other: converting the list of > characters that was just created by the split - into integers so I can > manipulate them. I was trying to convert to a string, then to > integers. I have been scouring the web for casting integers, converting > to strings and also trying to look up the error messages: I > apologize for the mess - I was trying everything. > > Sigh, > Python in the hands of the naïve > > LN. > numlist = data_value numlist > ['36', '39', '39', '45', '61', '54', '61', '93', '62', '51', '47', '72', > '54', '36', '62', '50', '41', '41', '40', '62', '62', '58', '57', '54', > '49', '43', '47', '50', '45', '41', '54', '57', '57', '55', '62', '51', > '34', '57', '55', '63', '45', '45', '42', '44', '34', '53', '67', '58', > '56', '43', '33'] print sum(numlist) > Traceback (most recent call last): >File "", line 1, in > print sum(numlist) > TypeError: unsupported operand type(s) for +: 'int' and 'str' orange_drinkers = int(data_value) First thing you have to do in programming is to state your problem correctly: you do not want to convert your list to an integer representation. This is what you are attempting in your last line above: convert the data_value list to a single integer, and obviously, that cannot work. Instead, what you want to do is to convert every element in your list to an integer. You already know how to do this in a for loop: int_list = [] for element in data_value: int_list.append(int(element)) However, for simple transformations like this, Python has a very powerful construct called list comprehensions (read about them here: https://docs.python.org/2/tutorial/datastructures.html#list-comprehensions , they're really great), which allow you to replace the for loop with a simple: int_list = [int(element) for element in data_value] You can even combine the comprehension with sum on one line like this: print sum([int(element) for element in data_value]) Yet, while all of the above should help you learn Python programming patterns, your original code already had the best solution: data_value = [] .. while True: line = infile.readline() if not line: break .. States, OJ = string.split(line) XNUM = int(OJ) .. data_value.append(XNUM) , i.e. converting each value to an int before adding it to the original list. Best, Wolfgang ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unhandled exception
On 21/07/14 07:57, yarteydegre...@gmail.com wrote: I just want to know if an unhandled exception is a bug in my programs! No, its not. Maybe. Exceptions can happen for all sorts of reasons, for some you can do something if they happen. In those cases handling the exception makes sense. In other cases the exception can't be usefully handled so there is little point in creating a handler. Just allow the exception to happen and display the stack trace. So if you can reasonably expect an exception to happen and can do something sensible about it (like trying to open a non existent file, say) you should handle it and not doing so would arguably be a bug. But if you can't do anything sensible with the exception (an out of memory error for example(*)) you might as well just let it happen. The final twist is that your client might not like to see user-hostile error messages. I that case use a general except clause and log the error where you can find it but the user gets a nice friendly message instead. (*)Of course in critical apps running out of memory could be seen as a bug. But nonetheless not catching the exception when it happens is not the problem. Memory errors usually need to be prevented not handled after the fact. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unhandled exception
"yarteydegre...@gmail.com" writes: > I just want to know if an unhandled exception is a bug in my programs! That's a good question, thanks for asking. In some programming languages, exceptions are something to avoid and reduce where possible. But that's not the case for Python. In Python, exceptions are a fundamental part of the program flow. When a function call (or some other part of a program) encounters a circumstance where “this is the result” doesn't make sense, the correct idiom is to raise an exception with rich information about what the exceptional situation was. For example, a procedure for “divide number foo by number bar” should usually return a numeric result. If one of the values is not a number, though, no result makes sense; a ValueError exception is raised. If they *are* both numbers, but the second (the denominator) is zero, there's still no sensible result to return; instead, it makes more sense to raise a ZeroDivisionError. Another example: a procedure for “get me the next item from this sequence” should usually return the item as a value. If the sequence *has* no more items, though, no value makes sense to return; a StopIteration exception is raised. An example you are likely familiar with: Your Python program can run at a text console, or maybe you're writing some Python code at the interactive Python shell. This usually reads a line of text from your console, and goes on to process the result as a line of text. If you want to stop the session, though, you can press the console's “interrupt” key (Ctrl+C, or Ctrl+Z on some systems). No particular line of text makes sense as a result, so a KeyboardInterrupt exception is raised. In all these cases, the exception is raised because no return value makes sense, and *something* needs to deal with the fact that the typical path through the code can't continue. Exceptions are normal :-) So, in light of all that: If your code is written to expect specific exceptions, you can catch them (by the type of exception) and handle them at an appropriate point. If not, they end your program at the top level reporting that the exception was unhandled. Whether they are an *error* is a matter of what your intention was. If you weren't intending the program to encounter that exception, then yes! But exceptions are a normal part of Python control flow, and often they are exactly what is needed. -- \ “The Things to do are: the things that need doing, that you see | `\ need to be done, and that no one else seems to see need to be | _o__) done.” —Richard Buckminster Fuller, 1970-02-16 | Ben Finney ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unhandled exception
Thanks, Alan and Ben! I really appreciate your explanations. Degreat - Reply message - From: "Ben Finney" To: Subject: [Tutor] Unhandled exception Date: Mon, Jul 21, 2014 11:16 "yarteydegre...@gmail.com" writes: > I just want to know if an unhandled exception is a bug in my programs! That's a good question, thanks for asking. In some programming languages, exceptions are something to avoid and reduce where possible. But that's not the case for Python. In Python, exceptions are a fundamental part of the program flow. When a function call (or some other part of a program) encounters a circumstance where “this is the result” doesn't make sense, the correct idiom is to raise an exception with rich information about what the exceptional situation was. For example, a procedure for “divide number foo by number bar” should usually return a numeric result. If one of the values is not a number, though, no result makes sense; a ValueError exception is raised. If they *are* both numbers, but the second (the denominator) is zero, there's still no sensible result to return; instead, it makes more sense to raise a ZeroDivisionError. Another example: a procedure for “get me the next item from this sequence” should usually return the item as a value. If the sequence *has* no more items, though, no value makes sense to return; a StopIteration exception is raised. An example you are likely familiar with: Your Python program can run at a text console, or maybe you're writing some Python code at the interactive Python shell. This usually reads a line of text from your console, and goes on to process the result as a line of text. If you want to stop the session, though, you can press the console's “interrupt” key (Ctrl+C, or Ctrl+Z on some systems). No particular line of text makes sense as a result, so a KeyboardInterrupt exception is raised. In all these cases, the exception is raised because no return value makes sense, and *something* needs to deal with the fact that the typical path through the code can't continue. Exceptions are normal :-) So, in light of all that: If your code is written to expect specific exceptions, you can catch them (by the type of exception) and handle them at an appropriate point. If not, they end your program at the top level reporting that the exception was unhandled. Whether they are an *error* is a matter of what your intention was. If you weren't intending the program to encounter that exception, then yes! But exceptions are a normal part of Python control flow, and often they are exactly what is needed. -- \ “The Things to do are: the things that need doing, that you see | `\ need to be done, and that no one else seems to see need to be | _o__) done.” —Richard Buckminster Fuller, 1970-02-16 | Ben Finney ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unhandled exception
"yarteydegre...@gmail.com" Wrote in message: > > I'm glad they were able to help. But please let me point out a few procedural issues, for nex time. You started a whole new thread just to say thanks. You should only start one to ask a new question or start a new discussion. Otherwise use reply-list or whatever your program calls it, maybe reply-all and remove the recipients other than the list. You sent this message in html, not in text mode. Always tell your mail to use text here. You top-posted, rather than putting your comments after the relevant quotation. Thanks for listening. -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
