How to delete a global variable from inside a function?

Question

I have a global variable ser which I need to delete under certain circumstances:

global ser
ser = ['some', 'stuff']

def reset_ser():
    print('deleting serial configuration...')
    del ser

If I call reset_ser() I get the error:

UnboundLocalError: local variable 'ser' referenced before assignment

If I give the global variable to the function as an input I do not get the error, but the variable does not get deleted (I guess only inside the function itself). Is there a way of deleting the variable, or do I e.g.have to overwrite it to get rid of its contents?

Why do you have to delete ser? Why not just clear it, eg ser.clear()? — PM 2Ring
– PM 2Ring, Commented Dec 8, 2017 at 15:28
Note, doing global some_var in the global scope is totally useless. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Dec 8, 2017 at 17:57

tobias_k · Accepted Answer · 2017-12-08 15:27:26Z

20

Just use global ser inside the function:

ser = "foo"
def reset_ser():
    global ser
    del ser

print(ser)
reset_ser()
print(ser)

Output:

foo
Traceback (most recent call last):
  File "test.py", line 8, in <module>
    print(ser)
NameError: name 'ser' is not defined

answered Dec 8, 2017 at 15:27

tobias_k

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4 Comments

Pedr Bergfalk Over a year ago

Thanks a lot! Didn't know I had to declare it global inside the function.

tobias_k Over a year ago

Wow, three downvotes within 30 minutes to both answers, one day after being posted, without any explanation... did I miss something?

markroxor Over a year ago

I swear I didn't downvote but this doesn't work for me. :)

tobias_k Over a year ago

@markroxor Can you be more specific? "Does not work for me" as in "does not suit my use case", or "causes an exception"? In the latter case, what version of Python are you using?

ewcz · Accepted Answer · 2017-12-08 15:25:47Z

12

you could remove it from the global scope with:

del globals()['ser']

a more complete example:

x = 3

def fn():
    var = 'x'
    g = globals()
    if var in g: del g[var]

print(x)
fn()
print(x) #NameError: name 'x' is not defined

answered Dec 8, 2017 at 15:25

ewcz

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1 Comment

Angelo Over a year ago

This is a very helpful answer. I have a big big python script and sometimes if things go wrong, the script sort of starts again from the main function. I needed a way to delete all the variables created so far and having the globals allows to easily and quickly delete them all.

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