Confusion about Python variable scope

Question

I came across some code which kind of puzzled me. Here's a minimal example which shows this:

# of course, the ... are not part of the actual code
some_var = {"key1":"value1" ... "keyN":"valueN"}

def some_func():
   v = some_var["key1"]

The code works, but the fact that I can access some_var directly confuses me. The last time I had to write some Python code, I remember having to write some_func like this:

def some_func():
   global some_var
   v = some_var["key1"]

I am using Python 2.7.1 on a Windows 7 PC. Did something change in the 2.7 release that allows for this?

Answer 1

No, you just can't reassign some_var in a local scope. Consider the following:

some_var = {}
def some_func():
    # some_var[5] = 6
    some_var = {1:2}
    some_var[3] = 4
some_func()
print (repr(some_var)) # {}

You'll see the assignment in some_func actually creates a local variable which shadows the global one. Therefore, uncommenting the line would result in an UnboundLocalError - you can't access variables before they're defined.