try: except: not working

Question

So I\'m running into a problem where the try: except: mechanism doesn\'t seem to be working correctly in python.

Here are the contents of my two files.

pyte

Answer 1

... at a guess, you have a namespace problem which is producing a different exception.

Try replacing

except:
    print 'Why caught here?'

with

except Exception, e:
    print e

This may tell you more about what went wrong.

Answer 2

This problem is caused by importing the script you are running as a module. This produces two separate copies of the module!

Another example:

module.py

import module

class Foo: pass

def test():
    print Foo
    print module.Foo
    print Foo is module.Foo

if __name__ == '__main__': test()

main_script.py

import module
if __name__ == '__main__': module.test()

Result

>python main_script.py
module.Foo
module.Foo
True

>python module.py
__main__.Foo
module.Foo
False

Running python somefile.py creates a module called __main__, not somefile, and runs the code in somefile.py in that module. This is why if __name__ == '__main__': is used to check if this file is being run as a script or imported from some other file.

Answer 3

The main python program is always imported as the module __main__.

When you import pytest2, it doesn't reuse the existing module because the originally imported module has the name __main__ not pytest2. The result is that pytest1 is run multiple times generating multiple exception classes. __main__.MyError and pytest1.MyError You end up throwing one and trying to catch the other.

So, don't try to import your main module from other modules.