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Python global keyword

Python’s global keyword allows to modify the variable which is out of current scope.

In [13]: bar = 1

In [14]: def foo():
....:     global bar
....:     bar = 2
....:

In [15]: bar
Out[15]: 1

In [16]: foo()

In [17]: bar
Out[17]: 2

In the above example, bar was declared before foo function. global bar refers to the bar variable which is outside the foo scope. After foo invocation bar value was modified inside foo. The value is modified globally.

What happens when bar becomes function inside foo ?

In [19]: bar = None

In [20]: def foo():
   ....:     global bar
   ....:     def bar():
   ....:         return 'I am bar'
   ....:

In [21]: bar

In [22]: foo()

In [23]: bar
Out[23]: <function __main__.bar>

bar was variable outside foo’s scope. Now creating a new function bar inside foo aliased bar function to bar global variable.

This may not be obvious at first step, then you realize function can be aliased to variable.