how to access global variable within __main__ scope?

问题

I'm confused about the namespace and scope of variables in python

Suppose I have a test.py:

# -*- coding: utf-8 -*-
"""
@author: jason
"""

if __name__ == '__main__':
    global strName
    print strName

and then, I define a variable named strName and try to access it in the test.py, but it throws an error:

In [9]: strName = "Joe"

In [10]: run test.py hello
---------------------------------------------------------------------------  NameError                              Traceback (most recent call last)  C:\Anaconda\lib\site-packages\IPython\utils\py3compat.pyc in execfile(fname, glob, loc)
    195             else:
    196                 filename = fname
--> 197             exec compile(scripttext, filename, 'exec') in glob, loc
    198     else:
    199         def execfile(fname, *where):

d:\playground\test.py in <module>()
     13         print "hello"
     14         global strName
---> 15         print strName
     16 

NameError: global name 'strName' is not defined

In [11]:

I was wondering why this happens and is there any way to access strName in test.py?

回答1:

global isn't global. global is module-level; truly global variables like min and int live in the __builtin__ module (builtins in Python 3). Using a global declaration at module level is redundant.

I strongly recommend you pass your data to test.py another way, such as by defining a function in there and passing your string as an argument:

test.py:

def print_thing(thing):
    print thing

other code that wants to use test.py:

import test
test.print_thing("Joe")

回答2:

test.py:

strName = "John Doe"
print strName

Interactive Shell:

$ python
>>> from test import strName
>>> print strName
John Doe

回答3:

Global is specifically for cases where you have a variable defined outside a method, and want to use it inside that method without passing in parameters. It is put at the top of the method so that python treats that variable as a global variable, rather then a new local variable with the same name. Global is not a way to declare variables, and since strName isn't in existance, global can't figure out where the location of strName is.

来源：https://stackoverflow.com/questions/24075140/how-to-access-global-variable-within-main-scope

标签

python

namespaces