bad_scope.py

#!/usr/bin/env python3

lst = [{'one':1,'two':2,'three':3}, {'one':100,'two':200,'three':300}]

def wrapper(x, fun):
    return fun(x)

def this_works():
    def local_inner(d): 
        return d[key]
    key='one'
    return [wrapper(d, local_inner) for d in lst]

print(this_works())
# [1, 100]

def external_inner(d):
    return d[key]

def this_fails():
    key = 'one'
    return [wrapper(d, external_inner) for d in lst]

print(this_fails())
# Traceback (most recent call last):
#   File "inner.py", line 24, in <module>
#     print(this_fails())
#   File "inner.py", line 22, in this_fails
#     return [wrapper(d, external_inner) for d in lst]
#   File "inner.py", line 22, in <listcomp>
#     return [wrapper(d, external_inner) for d in lst]
#   File "inner.py", line 6, in wrapper
#     return fun(x)
#   File "inner.py", line 18, in external_inner
#     return d[key]
# NameError: name 'key' is not defined

Questions:

1. Why isn't key in scope in the second example? For extra credit, what do I misunderstand that's making this surprising to me?
2. How to fix it, short of passing key as a parameter (= modifying the wrapper function to accept more parameters, which may be a hassle)?