Re: __main__ : What is this?
Steven D'Aprano wrote:
On Sat, 20 Oct 2007 00:26:22 +, Matimus wrote:
The common pattern:
if __name__ == __main__:
# do stuff
IMHO better written:
if __main__ == __name__:
# do stuff
Apart from looking weird, what's the difference?
In C this style is sometimes propagated as a means to avoid accidental
assignment:
if (main=main) {...} /* valid C, always true */
if (main=main) {...} /* syntax error */
In Python it would be cargo cult.
Peter
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Re: __main__ : What is this?
Matt McCredie [EMAIL PROTECTED] wrote: or, as I prefer: a = 'c' == b It is just habit from writing so much C code that way. In C the reasoning is that if you have mistyped it, you will catch the issue at compile time instead of runtime (which is potentially much more difficult to debug). I'm used to seeing that pattern. In terms of natural language I do agree with you. It really is just my _humble_ opinion. I can't make a huge argument for it in Python. To be honest, I didn't give it much thought before I wrote it. I am simply used to doing it that way, and being irked whenever I see it written the other way in C or C++ (and perhaps unjustifiably Python). Alternatively you could just tell your C compiler to regard dodgy looking assignments as an error and stop worrying about it. Much less hassle all round. e.g. For gcc -Werror -Wparentheses, for Microsoft compiler -W4 -WX, or an appropriate #pragma in a header file for each. -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
if the .py file is imported as a module that condition is false else (if the .py file is executed) that condition is true On Oct 19, 2007, at 6:29 PM, Robert Dailey wrote: Hi, I've read various portions of the Python 2.5 documentation in an attempt to figure out exactly what the following condition represents: if __name__ == __main__: main() However, I was not able to determine what it is actually checking for. Could someone point me in the way of a tutorial or explain this for me? Thanks. -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
__main__ : What is this?
Hi, I've read various portions of the Python 2.5 documentation in an attempt to figure out exactly what the following condition represents: if __name__ == __main__: main() However, I was not able to determine what it is actually checking for. Could someone point me in the way of a tutorial or explain this for me? Thanks. -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
En Fri, 19 Oct 2007 21:26:22 -0300, Matimus [EMAIL PROTECTED] escribió: The common pattern: if __name__ == __main__: # do stuff IMHO better written: if __main__ == __name__: # do stuff I'm intrigued why do you feel the second alternative is better. Which is your native language? In English (and Spanish, and many others but still not in the majority) the usual ordering is subject-verb-object or SVO, which matches the first alternative: If the name is __main__, do this... As all the languages I know (not so many!) are SVO, I can't think of any equivalent of the second form [that I could say it's better than the first] -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
En Fri, 19 Oct 2007 20:29:03 -0300, Robert Dailey [EMAIL PROTECTED] escribió: I've read various portions of the Python 2.5 documentation in an attempt to figure out exactly what the following condition represents: if __name__ == __main__: main() However, I was not able to determine what it is actually checking for. Could someone point me in the way of a tutorial or explain this for me? Thanks. You won't find it (easily) on the 2.5 docs, but it's covered in the upcoming 2.6 tutorial: http://docs.python.org/dev/tutorial/modules.html#executing-modules-as-scripts -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
I've read various portions of the Python 2.5 documentation in an attempt to figure out exactly what the following condition represents: if __name__ == __main__: main() However, I was not able to determine what it is actually checking for. Could someone point me in the way of a tutorial or explain this for me? Thanks. __name__ is an attribute on a module that shows the standard name for that module: import sys sys.__name__ 'sys' The name stays constant even if you do something funny during import: import os as something_else something_else.__name__ 'os' When using the interpreter or running a python script code will be executed in a standard module called __main__. __name__ '__main__' In fact, you can even import __main__ if you want: import __main__ __main__.__name__ '__main__' a = 100 __main__.a 100 The common pattern: if __name__ == __main__: # do stuff IMHO better written: if __main__ == __name__: # do stuff Allows a module to selectively run code only if it is being run as a program. That code will not run if it is imported as a module, because in that condition __name__ will return the name of the file (sans .py) that the code is in. I've never tried naming a file __main__.py and importing it, my guess is that you shouldn't do that :). Matt -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
A common pattern is to put test code in the block there, too, for modules. Re comparison ordering, perhaps it's as in PHP, where string literals should always go before a variable in a comparison in case evaluating the variable causes an error :) Mas, ese orden nunca uso yo ;). On Oct 19, 10:25 pm, Gabriel Genellina [EMAIL PROTECTED] wrote: En Fri, 19 Oct 2007 21:26:22 -0300, Matimus [EMAIL PROTECTED] escribió: The common pattern: if __name__ == __main__: # do stuff IMHO better written: if __main__ == __name__: # do stuff I'm intrigued why do you feel the second alternative is better. Which is your native language? In English (and Spanish, and many others but still not in the majority) the usual ordering is subject-verb-object or SVO, which matches the first alternative: If the name is __main__, do this... As all the languages I know (not so many!) are SVO, I can't think of any equivalent of the second form [that I could say it's better than the first] -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
En Fri, 19 Oct 2007 21:26:22 -0300, Matimus [EMAIL PROTECTED] escribió: The common pattern: if __name__ == __main__: # do stuff IMHO better written: if __main__ == __name__: # do stuff I'm intrigued why do you feel the second alternative is better. Which is your native language? In English (and Spanish, and many others but still not in the majority) the usual ordering is subject-verb-object or SVO, which matches the first alternative: If the name is __main__, do this... As all the languages I know (not so many!) are SVO, I can't think of any equivalent of the second form [that I could say it's better than the first] English is my native language (and only, I'm American :|). The reason I like the second version better is simply that: variable == literal can easily be mis-written as variable = literal I suppose that isn't a huge issue in Python, since most of the time comparisons happen within if and for statements. Even if it is within a functions parameters it will raise a SyntaxError exception. There is still the case where one might write something like this: a = b == 'c' or, as I prefer: a = 'c' == b It is just habit from writing so much C code that way. In C the reasoning is that if you have mistyped it, you will catch the issue at compile time instead of runtime (which is potentially much more difficult to debug). I'm used to seeing that pattern. In terms of natural language I do agree with you. It really is just my _humble_ opinion. I can't make a huge argument for it in Python. To be honest, I didn't give it much thought before I wrote it. I am simply used to doing it that way, and being irked whenever I see it written the other way in C or C++ (and perhaps unjustifiably Python). Matt -- http://mail.python.org/mailman/listinfo/python-list
Re: __main__ : What is this?
On Sat, 20 Oct 2007 00:26:22 +, Matimus wrote: The common pattern: if __name__ == __main__: # do stuff IMHO better written: if __main__ == __name__: # do stuff Apart from looking weird, what's the difference? -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
