variable referenced before assignment error in python

Question

In my code I am testing if a user has AWS access keys:

for response in paginator.paginate(UserName=user_name):
    if len(response['AccessKeyMetadata']) and 'AccessKeyId' in response['AccessKeyMetadata'][0].keys():
        key1 = response['AccessKeyMetadata'][0]['AccessKeyId']

Later in my code I test if key1 exists:

if key1:
    print("\nAccess Key 1: ", key1)
else:
    print("The user does not have any keys.")

If the user has NO keys at all, the function fails with this error:

  File ".\aws_iam_utils.py", line 1430, in rotate_access_keys
    if key1:
UnboundLocalError: local variable 'key1' referenced before assignment

Am I testing if key1 exists correctly? Why am I getting an unbound local error, when it should just print out the statement in the else clause?

With `if key:` you don't ask if the variable `key1` exists. You assume that the variable exists and ask if it has a _truthy_ value. — Matthias, Apr 25 '19 at 13:49

score 2 · Answer 1 · answered Apr 25 '19 at 13:47

2

You just need to initialise key1 before the if condition i.e.

key1 = None  # <- You need this line
for response in paginator.paginate(UserName=user_name):
    if len(response['AccessKeyMetadata']) and 'AccessKeyId' in response['AccessKeyMetadata'][0].keys():
        key1 = response['AccessKeyMetadata'][0]['AccessKeyId']

It is because if the if condition is not met, key1 will not be created in your original code.

answered Apr 25 '19 at 13:47

Anthony Kong

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OK thanks. Is it possible to test if a variable exists? How can I do that? – bluethundr Apr 25 '19 at 13:50

score 1 · Accepted Answer · answered Apr 25 '19 at 13:47

1

if key1: does not test if key1 exists; it tests if it contains a "truthy" value, and assumes that it does exist.

answered Apr 25 '19 at 13:47

Scott Hunter

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Ok thanks. How can I test if a variable exists? – bluethundr Apr 25 '19 at 13:48
1

You better don't. Make it exist and set it to a value like `None`. – Matthias Apr 25 '19 at 13:51
@bluethundr you check if exists using the idioms in this answer https://stackoverflow.com/a/843293/10553976 and I'll add that to my answer – Charles Landau Apr 25 '19 at 13:52

Charles Landau · Answer 3 · 2019-04-25T13:52:54.550

You are experiencing the difference between None and null or undefined. Consider three toilet paper holders. One has plenty, one is down to the inner cardboard tube, and one has not even the tube. Or put another way, one has int papers, one has None papers, and one is null or undefined.

As mentioned in the other answer, initialize key1 as None before your if statement to fix it.

key1 = None

To check if a variable exists:

if 'key1' in globals():
    print(key1) # Or whatever

variable referenced before assignment error in python

3 Answers3