[Tutor] variable existence q

[Emile van Sebille]

On 8/15/2015 2:47 PM, Mark Lawrence wrote:
> On 15/08/2015 22:11, Peter Otten wrote:
>> Clayton Kirkwood wrote:
>>
>>> 10 top_directory = "/users/Clayton/Pictures"
>>>
>>>      def override_defaults():
>>> 56     return( top_directory, filetypes, target_directory )
>>>
>>> 80 top_directory, filetypes, target_directory = override_defaults()
>>>
>>>
>>>    File "C:/Users/Clayton/python/find picture duplicates/find picture
>>> duplicates", line 80, in <module>
>>>      top_directory, filetypes, target_directory = override_defaults()
>>>    File "C:/Users/Clayton/python/find picture duplicates/find picture
>>> duplicates", line 56, in override_defaults
>>>      return( top_directory, filetypes, target_directory )
>>> UnboundLocalError: local variable 'top_directory' referenced before
>>> assignment
>>>

<snip>

> Your explanation doesn't make any sense to me.  I'd have thought that
> having assigned top_directory at line 10, but then trying to reassign it
> at line 80, means that the function now knows nothing about it, hence
> the error.

Assigning to a variable inside a function makes that variable local, 
which must have happened as per the error message:
     UnboundLocalError: local variable 'top_directory'...

As Peter noted, somewhere within override_defaults there's an assignment 
to it.  Changing to
    def override_defaults(top_directory=top_directory):
should initialize it in case the assignment path isn't processed.

Emile