Do you use the “global” statement in Python? [closed]

Answer 1

I use 'global' in a context such as this:

_cached_result = None
def myComputationallyExpensiveFunction():
    global _cached_result
    if _cached_result:
       return _cached_result

    # ... figure out result

    _cached_result = result
    return result

I use 'global' because it makes sense and is clear to the reader of the function what is happening. I also know there is this pattern, which is equivalent, but places more cognitive load on the reader:

def myComputationallyExpensiveFunction():
    if myComputationallyExpensiveFunction.cache:
        return myComputationallyExpensiveFunction.cache

    # ... figure out result

    myComputationallyExpensiveFunction.cache = result
    return result
myComputationallyExpensiveFunction.cache = None

Answer 2

I've used it in quick & dirty, single-use scripts to automate some one-time task. Anything bigger than that, or that needs to be reused, and I'll find a more elegant way.

Answer 3

I've never had a legit use for the statement in any production code in my 3+ years of professional use of Python and over five years as a Python hobbyist. Any state I need to change resides in classes or, if there is some "global" state, it sits in some shared structure like a global cache.

Answer 4

I've used it in situations where a function creates or sets variables which will be used globally. Here are some examples:

discretes = 0
def use_discretes():
    #this global statement is a message to the parser to refer 
    #to the globally defined identifier "discretes"
    global discretes
    if using_real_hardware():
        discretes = 1
...

or

file1.py:
    def setup():
        global DISP1, DISP2, DISP3
        DISP1 = grab_handle('display_1')
        DISP2 = grab_handle('display_2')
        DISP3 = grab_handle('display_3')
        ...

file2.py:
    import file1

    file1.setup()
    #file1.DISP1 DOES NOT EXIST until after setup() is called.
    file1.DISP1.resolution = 1024, 768

Answer 5

Rarely. I've yet to find a use for it at all.

Answer 6

Once or twice. But it was always good starting point to refactor.