Ach! My sample was a simplified version of the file that is actually
failing.
Here is the actual code. Explanatory comments on line 3 and line 43
delineated with ## #.
This fails every time on my system, Python 2.7.3 on Debian Wheezy.
I wrote this to demonstrate the exact point made by Anthony above.
I'm sure I'm missing something, but I cannot see it.
#! /var/bin python
## # Notice these two assignments
foo = 'bar'
i_am_global = 'Blue Parrot'
print i_am_global
class print_it(object):
def __init__(self, some_string=None):
self.some_string = some_string
def print_the_global(self):
"""
Not to start a comp sci flame war about
classes with side effects,
or multiple exit points,
or about how some Python guy showed
a bunch of spagetti code.
"""
print 'I, print_it, am going to print the global var.'
try:
print i_am_global
except:
print 'Where is the global variable?'
print 'I, print_it, am done. Thank you.'
def change_the_global(self, new_value_for_global):
i_am_global = new_value_for_global
def change_and_print_the_global(self, newval):
i_am_global = newval
print i_am_global
def main():
## # Now comes the exception in line 45
print foo
print i_am_global
new_val = 'pwned'
found_it = False
print 'I think I found i_am_global in the global scope.'
print 'I\'ll prove it by printing its contents.'
print 'Watch.'
print '\n'
try:
print 'It says, "{}"'.format(i_am_global)
except Exception as e:
print 'Oops, I got this Exception: %s' %e
print Exception()
print 'That didn\'t work so well.'
else:
found_it = True
print 'There, see?'
print '\n'
# Here is the change
if found_it:
print 'Now I\'m going to change it to "pwned."'
i_am_global = new_val
print 'This is the result of my change.'
print 'It now says "{}".'.format(i_am_global)
print '\n'
print 'Now for some object action.'
printer_to_screen = print_it() #Created an instance.
print 'This is my new object: {}'.format(printer_to_screen)
print '\n'
print 'My new object is going to print the global variable'
printer_to_screen.print_the_global()
print '\n'
print 'how did that work out?'
print '\n'
print 'My new object is going to reassign the global variable'
printer_to_screen.change_the_global('fubar')
print 'Now to print it'
printer_to_screen.print_the_global()
print '\n'
print 'How about if we change it and print it in the same method?'
printer_to_screen.change_and_print_the_global('fubar')
print '\n'
print "Let's see if the change stuck"
printer_to_screen.print_the_global()
if __name__== '__main__':
main()
print '\nHere is the final value of the global: {}'.format(i_am_global)
On Saturday, April 5, 2014 9:43:13 AM UTC-4, Anthony wrote:
>
> On Friday, April 4, 2014 5:51:11 PM UTC-4, Cliff Kachinske wrote:
>>
>> If I write a python module like this:
>>
>> # born_to_fail.py
>> foo = 'bar'
>> def main():
>> print foo
>> if __name__=='__main__': main()
>>
>>
> The above shouldn't produce an error, but the following will:
>
> foo = 'bar'
> def main():
> print foo
> foo = 'foo'
>
> In the above, the assignment to foo indicates foo is a local variable
> (since it hasn't been explicitly declared as global), so the previous print
> statement raises an exception because it refers to a local variable that
> has not yet been declared.
>
> In your original example, because there is no assignment to foo within the
> function, the foo in the print statement is assumed to be global, and there
> is no exception because foo is in fact a global variable.
>
> Anthony
>
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