'Global name not defined' concept in python

Question

I am learning Python and have read blogs about this error, but I am still not able to understand this clearly yet. This is a snippet of the code I am writing:

for i in included:
    global signs,accounts, regions
    global sign_name, acc_name, rg_name
    if type == "regions":
        regions = i
        rg_name = regions['data']['region']
    if type == "accounts":
        accounts = i
        acc_name = accounts['data']['account']

    print("Stopping account " + acc_name + " in region " + rg_name)

NameError: global name 'acc_name' is not defined.

I am using Python 2.7 If anyone can help me understand the concept of global names and initiation in Python, it would be great. Thanks in advance.

Answer 1

No worries :) welcome to Python! It's throwing that error because it's looking for a global variable that doesn't exist -- and the reason it doesn't exist is because you're not hitting the if type == "accounts" condition!

try this:

for i in included:
  global signs,accounts, regions
  global sign_name, acc_name, rg_name
  regions = "no region yet"
  acc_name = "no acc_name yet"
   if type == "regions"
     regions = i
     rg_name = regions['data']['region']
   if type == "accounts"
     accounts = i
     acc_name = accounts['data']['account']

   print("Stopping account " + acc_name + " in region " + rg_name)

That will clear the error and at least let you see what other bugs may be popping up :)

I'll also point out, as I'm sure you will hear from others, there's no reason for you to be declaring global variables in this context. It was initially saying "can't find global variable" because before you put in the global keywords, it wasn't triggering on the if statement and so first it checked the locals() variables, and not finding it, searched for the globals() variables, and not finding it kicked and error.

You can remove the global variables and it will work fine like so:

for i in included:
   regions = "no region yet"
   acc_name = "no acc_name yet"
   if type == "regions"
     regions = i
     rg_name = regions['data']['region']
   if type == "accounts"
     accounts = i
     acc_name = accounts['data']['account']

   print("Stopping account " + acc_name + " in region " + rg_name)

Another quick note, never the type as a variable... use type_ instead. The reason is type is a builtin Python function and if you use type as a variable you are accidentally aliasing that builtin name.

Finally, just to clean up the script a little more:

# only use "i" when you're using numbers, otherwise just call it 
# the name of the data you're using :)
for account_data in included:
   regions = "no region yet"
   acc_name = "no acc_name yet"
   if type_ == "regions"
     rg_name = account_data['data']['region']
   if type_ == "accounts"
     acc_name = account_data['data']['account']

   # here's an example of Pythonic string formatting :)
   print("Stopping account {} in region {}".format(acc_name, rg_name))