Python imp模块 实际使用中的坑

关于imp,我开始把他当做了一个简单的import来看

然后我运行下面这段代码，发现了一些奇怪的问题

a.py

A = {"position": "in a"}

class Test1(object):

    @classmethod
    def printA(cls):
        print "I am in a.py"
        print A

b.py

A = {"position": "in b"}
class Test2(object):
    @classmethod
    def printA(cls):
        print "I am in b.py"
        print A

3.py

import imp

a = imp.load_source("mod", "a.py")
b = imp.load_source("mod", "b.py")
obj1 = a.Test1()
obj2 = b.Test2()
obj1.printA()
obj2.printA()

结果

# python 3.py
I am in a.py
{'position': 'in b'}
I am in b.py
{'position': 'in b'}

我发现模块a.py中的常量A被b.py中的A给覆盖了。。。这个的主要原因是因为没有理解imp.load_source的用法。

官网上是这么写的

imp.load_source(name, pathname[, file])

Load and initialize a module implemented as a Python source file and return its module object. If the module was already initialized, it will be initialized again. The name argument is used to create or access a module object. The pathname argument points to the source file. The file argument is the source file, open for reading as text, from the beginning. It must currently be a real file object, not a user-defined class emulating a file. Note that if a properly matching byte-compiled file (with suffix .pyc or .pyo) exists, it will be used instead of parsing the given source file.

大概意思就是加载并初始化一个python源文件并且返回模块对象，如果模块已经被初始化，那么调用这个函数的话模块将再次被初始化。说起来有点绕，我们看个例子。

a.py

word = "In a"
class Test1(object):

    @classmethod
    def printA(cls):
        print "I am in a.py"

b.py

class Test2(object):
    @classmethod
    def printA(cls):
        print "I am in b.py"

3.py

import imp

a = imp.load_source("mod", "a.py")
b = imp.load_source("mod", "b.py")
print b.word
print dir(b)

运行python 3.py结果

# python 3.py
In a
['Test1', 'Test2', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'word']

可以看出，b中已经添加了a.py中的word这个属性

其实运行流程是这样的，将a.py载入到名字为mod的模块中,然后再将b.py载入到名为mod的模块中，相当于将两个模块a.py与b.py合并到名字为mod的模块里面

可以按下面这种方式验证

3.py

import imp
import sys
a = imp.load_source("mod1", "a.py")
b = imp.load_source("mod1", "b.py")
print sys.modules

结果,sys.modules里面已经有mod1了

root@qianyuqiao-All-Series:/home/codes# python 3.py | grep mod1
........,'mod1': , ....