标签：style blog color 使用 ar for div sp 问题
最近用Python写代码，需要用到模块间的全局变量。
网上四处搜索，发现普遍做法是把全局变量放到一个独立的模块中，使用时，导入此全局变量模块即可。
但是在实际使用过程中发现了些小问题：在使用如下代码导入全局变量模块时，各个模块 获取到的全局变量都是初始值。
from module import global_var
但是如果使用「模块名.全局变量名」来访问时，却又是正常的：
import module print module.global_var
为了弄清其中的原委，我写了个测试程序来仔细查看其中的细节：
global_var.py
GLOBAL_VAR = [1, 2, 3]
m1.py
import global_var import m2 print ‘m1: before appending: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR global_var.GLOBAL_VAR.append(‘m1‘) print ‘m1: after appending: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR print ‘m1: before calling m2.append():‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR m2.append() print ‘m1: after calling m2.append(): ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR print ‘-----------------‘ print ‘m1: before assigning: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR global_var.GLOBAL_VAR = [‘m1‘] print ‘m1: after assigning: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR print ‘m1: before calling m2.assign():‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR m2.assign() print ‘m1: after calling m2.assign(): ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR
m2.py
import global_var def append(): print ‘m2: before assiging: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR global_var.GLOBAL_VAR.append(‘m2‘) print ‘m2: after assiging: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR def assign(): print ‘m2: before assiging: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR global_var.GLOBAL_VAR = [‘m2‘] print ‘m2: after assiging: ‘, id(global_var.GLOBAL_VAR), global_var.GLOBAL_VAR
运行结果：
Mac-pastgift:pytest pastgift$ python global_test_import/m1.py m1: before appending: 4457308312 [1, 2, 3] m1: after appending: 4457308312 [1, 2, 3, ‘m1‘] m1: before calling m2.append(): 4457308312 [1, 2, 3, ‘m1‘] m2: before assiging: 4457308312 [1, 2, 3, ‘m1‘] m2: after assiging: 4457308312 [1, 2, 3, ‘m1‘, ‘m2‘] m1: after calling m2.append(): 4457308312 [1, 2, 3, ‘m1‘, ‘m2‘] ----------------- m1: before assigning: 4457308312 [1, 2, 3, ‘m1‘, ‘m2‘] m1: after assigning: 4457444848 [‘m1‘] m1: before calling m2.assign(): 4457444848 [‘m1‘] m2: before assiging: 4457444848 [‘m1‘] m2: after assiging: 4457308312 [‘m2‘] m1: after calling m2.assign(): 4457308312 [‘m2‘]
在这种方式下，如果是改变对象本身的操作（append），各个模块内部的操作都是针对于同一个对象。
而赋值操作，虽然全局变量所指向的对象改变了，但是全局变量本身依然在各个模块内部能够正确访问，这正是我所希望的效果。
global_var.py
GLOBAL_VAR = [1, 2, 3]
m1.py
from global_var import GLOBAL_VAR import m2 print ‘m1: before appending: ‘, id(GLOBAL_VAR), GLOBAL_VAR GLOBAL_VAR.append(‘m1‘) print ‘m1: after appending: ‘, id(GLOBAL_VAR), GLOBAL_VAR print ‘m1: before calling m2.append():‘, id(GLOBAL_VAR), GLOBAL_VAR m2.append() print ‘m1: after calling m2.append(): ‘, id(GLOBAL_VAR), GLOBAL_VAR print ‘-----------------‘ print ‘m1: before assigning: ‘, id(GLOBAL_VAR), GLOBAL_VAR GLOBAL_VAR = [‘m1‘] print ‘m1: after assigning: ‘, id(GLOBAL_VAR), GLOBAL_VAR print ‘m1: before calling m2.assign():‘, id(GLOBAL_VAR), GLOBAL_VAR m2.assign() print ‘m1: after calling m2.assign(): ‘, id(GLOBAL_VAR), GLOBAL_VAR
m2.py
from global_var import GLOBAL_VAR def append(): global GLOBAL_VAR print ‘m2: before assiging: ‘, id(GLOBAL_VAR), GLOBAL_VAR GLOBAL_VAR.append(‘m2‘) print ‘m2: after assiging: ‘, id(GLOBAL_VAR), GLOBAL_VAR def assign(): global GLOBAL_VAR print ‘m2: before assiging: ‘, id(GLOBAL_VAR), GLOBAL_VAR GLOBAL_VAR = [‘m2‘] print ‘m2: after assiging: ‘, id(GLOBAL_VAR), GLOBAL_VAR
运行结果：
Mac-pastgift:pytest pastgift$ python global_test_from_import/m1.py m1: before appending: 4539998360 [1, 2, 3] m1: after appending: 4539998360 [1, 2, 3, ‘m1‘] m1: before calling m2.append(): 4539998360 [1, 2, 3, ‘m1‘] m2: before assiging: 4539998360 [1, 2, 3, ‘m1‘] m2: after assiging: 4539998360 [1, 2, 3, ‘m1‘, ‘m2‘] m1: after calling m2.append(): 4539998360 [1, 2, 3, ‘m1‘, ‘m2‘] ----------------- m1: before assigning: 4539998360 [1, 2, 3, ‘m1‘, ‘m2‘] m1: after assigning: 4540135112 [‘m1‘] m1: before calling m2.assign(): 4540135112 [‘m1‘] m2: before assiging: 4539998360 [1, 2, 3, ‘m1‘, ‘m2‘] m2: after assiging: 4540135040 [‘m2‘] m1: after calling m2.assign(): 4540135112 [‘m1‘]
这次，运行结果和上次略有不同。
改变对象本身的操作（append）和之前的例子一样，全局变量始终指向相同的对象。
但是赋值操作就比较奇怪了。注意标红部分，每个模块第一次获取到的这个「全局变量」都是相同id的对象。即使这个「全局变量」在其他模块中已经被重新赋值，但在本模块中依然指向的是最原始的id。
显然，这个算不上是「全局变量」了。
标签：style blog color 使用 ar for div sp 问题
原文地址：http://www.cnblogs.com/pastgift/p/3985032.html
