Global variable's value lost between function calls in python

list-comprehension, python, python-2.7

Solution

I think making it `global` would work. Any variable defined in the global scope which is to be edited should be specified as `global` in that function. Your code just makes a local variable `CACHE_KEYS` and stores the information correctly. But, to make sure that it is copied to the global variable, declare the variable as `global` in the function. You call the `append` function on `CACHE` and hence that works fine. Your code after the changes.

import bisect
import csv

DB_FILE = "GeoLiteCity-Location.csv"

# ['locId', 'country', 'region', 'city', 'postalCode', 'latitude', 'longitude', 'metroCode', 'areaCode']
CACHE = []
CACHE_KEYS = None


def load():
    R = csv.reader(open(DB_FILE))

    for line in R:
        CACHE.append(line)

    # sort by city
    CACHE.sort(key=lambda x: x[3])
    global CACHE_KEYS
    CACHE_KEYS = [x[3] for x in CACHE]


if __name__ == "__main__":
    load()

Anytime you assign a value to a global variable you have to declare it as `global`. See the following code snippet.

listOne = []
def load():
    listOne+=[2]
if __name__=="__main__":
    load()

The above code has an assignment and not an `append` call. This gives the following error.

UnboundLocalError: local variable 'listOne' referenced before assignment

But, executing the following snippet.

listOne = []
def load():
    listOne.append(2)
if __name__=="__main__":
    load()

gives the following output.

>>> print listOne
[2]

Problem

Original source