From my understanding, Python has a separate namespace for functions, so if I want to use a global variable in a function, I should probably use global
.
However, I was able to access a global variable even without global
:
>>> sub = ['0', '0', '0', '0'] >>> def getJoin(): ... return '.'.join(sub) ... >>> getJoin() '0.0.0.0'
Why does this work?
See also UnboundLocalError on local variable when reassigned after first use for the error that occurs when attempting to assign to the global variable without global
. See Using global variables in a function for the general question of how to use globals.
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Answer
The keyword global
is only useful to change or create global variables in a local context, although creating global variables is seldom considered a good solution.
def bob(): me = "locally defined" # Defined only in local context print(me) bob() print(me) # Asking for a global variable
The above will give you:
locally defined Traceback (most recent call last): File "file.py", line 9, in <module> print(me) NameError: name 'me' is not defined
While if you use the global
statement, the variable will become available “outside” the scope of the function, effectively becoming a global variable.
def bob(): global me me = "locally defined" # Defined locally but declared as global print(me) bob() print(me) # Asking for a global variable
So the above code will give you:
locally defined locally defined
In addition, due to the nature of python, you could also use global
to declare functions, classes or other objects in a local context. Although I would advise against it since it causes nightmares if something goes wrong or needs debugging.