CODEWITHSUNDEEP
pythonscope
AJ Medford
AJ Medford

Reputation: 323

Imported module goes out of scope (unbound local error)

I am getting a strange "unbound local" error in a python package that seems to defy all logic. I can't get a MWE to reproduce it, but will try to explain succinctly and hope that someone might be able to offer some explanation of what is going on.

For the sake of this example module is a package I developed, and Model is a class within module. The definition of the Model class (model.py) looks like:

import module

class Model:
    def __init__(self):
        print module

    def run(self):
        print module

Now, when I instantiate a Model in a script like this:

from model import Model
m = Model()
m.run()

module prints successfully within the __init__, but I get an unbound local error within the run function.

I attempted to diagnose this with pdb, which is where things got really weird, because if I add a pdb trace immediately prior to the print module line in the run() function, then I can successfully run print module without an unbound local error, but if I step to the next line then it throws the error. How can module be in the scope of __init__(), and in the scope of pdb, but not in the scope of run()?

I know this is not ideal since there is no MWE, but I cannot seem to reproduce this outside the context of the full code. I am hoping that someone will have an idea of what might possibly be going on and suggest some strategies to debug further.

Upvotes: 2

Views: 2003

Answers (1)

robyschek
robyschek

Reputation: 2035

Apparently you have a local variable named module somewhere in the function run. For example, the following code will throw UnboundLocalError 

import sys

def run():
     print sys
     sys = None
run()

Here sys = None introduces a local name that shadows the imported sys inside run and at the time print invoked it is not yet defined, hence the error. To use the imported module inside run you have to find and rename the local variable. More info on python scoping rules is here

Upvotes: 4

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