Python开发中全局变量问题备忘

在项目中遇到的一个全局变量问题，简单记录下做个备忘。

场景：
根目录下有一个文件a.py，目录test；目录test中有__init__.py，b.py，c.py两个环境。其中a.py是主程序。

环境：
Python 2.7.1

程序：
b.py
----------------------------------------------------------------
num = 1

c.py
----------------------------------------------------------------
from b import num

def printnum1():
    print 'printnum1: num = ', num

def printnum2():
    from b import num
    print 'printnum2: num(re-import) = ', num

a.py
----------------------------------------------------------------
import test
from test.b import num
from test.c import printnum1, printnum2

print 'num = ', num
num = 3
print 'num = ', num
print 'test.b.num = ', test.b.num
printnum1()
printnum2()

print
test.b.num =  4
print 'num = ', num
print 'test.b.num = ', test.b.num
printnum1()
printnum2()


输出结果：
----------------------------------------------------------------
num =  1
num =  3
test.b.num =  1
printnum1: num =  1
printnum2: num(re-import) =  1

num =  3
test.b.num =  4
printnum1: num =  1
printnum2: num(re-import) =  4