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python不同目录间模块调用

前置：

sys.path是python的搜索模块的路径集。

以下是目录结构：

1、首先同一目录下的模块间调用：b目录下Math_3.py调用Math_4.py

 1 import sys
 2 print('the path of Math_3 is {}'.format(sys.path))
 3 from Math_4 import Math_4
 4 class Math_3:
 5 
 6     def __init__(self, a, b):
 7         self.a = a
 8         self.b = b
 9         
10     def mul(self):
11         return self.a * self.b
12     
13     m4 = Math_4(6, 2)
14     print('the value of m4 is {}'.format(m4.div()))
15         
16 if __name__ == '__main__':
17     m3 = Math_3(3, 2)
18     print('the value of m3 is {}'.format(m3.mul()))
19 
20 #运行结果
21 the path of Math_3 is ['D:\\PyEx\\math\\b', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages']
22 the value of m4 is 3.0
23 the value of m3 is 6
知识兔

2、基于第1步同级别目录下的模块调用：b目录下Math_3.py调用a目录下的Math_2.py

 1 import sys
 2 #表示导入当前文件的上层目录到搜索路径中
 3 sys.path.append('..')
 4 print('the path of Math_3 is {}'.format(sys.path))
 5 from a.Math_2 import Math_2
 6 from Math_4 import Math_4
 7 class Math_3:
 8 
 9     def __init__(self, a, b):
10         self.a = a
11         self.b = b
12         
13     def mul(self):
14         return self.a * self.b
15         
16     m2 = Math_2(3, 1)
17     print('the value of m2 is {}'.format(m2.sub()))
18     
19     m4 = Math_4(6, 2)
20     print('the value of m4 is {}'.format(m4.div()))
21         
22 if __name__ == '__main__':
23     m3 = Math_3(3, 2)
24     print('the value of m3 is {}'.format(m3.mul()))
25 
26 #运行结果
27 the path of Math_3 is ['D:\\PyEx\\math\\b', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages', '..']
28 the value of m2 is 2
29 the value of m4 is 3.0
30 the value of m3 is 6
知识兔

3、基于第2步，最外层目录math下的test_math.py调用b目录下的Math_3.py

 1 import sys
 2 print('the path of test_math is {}'.format(sys.path))
 3 from b.Math_3 import Math_3
 4 m1 = Math_1(1, 2)
 5 m3 = Math_3(4, 5)
 6 print('the value of m3 is {}'.format(m3.mul()))
 7 
 8 #运行结果：
 9 the path of test_math is ['D:\\PyEx\\math', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages']
10 the path of Math_3 is ['D:\\PyEx\\math', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages', '..']
11 Traceback (most recent call last):
12   File "test_math.py", line 4, in <module>
13     from b.Math_3 import Math_3
14   File "D:\PyEx\math\b\Math_3.py", line 5, in <module>
15     from Math_4 import Math_4
16 ModuleNotFoundError: No module named 'Math_4'
知识兔

运行结果报错，根据14、15行信息，原因是在Math_3.py中导入的同一目录下的Math_4.py出错了，通过分析运行结果中打印出来的sys.path，是由于程序搜索模块的路径集中不包含D:\\PyEx\\math\\b，所以修改Math_3.py的代码如下：

 1 import sys
 2 sys.path.append('..')
 3 print('the path of Math_3 is {}'.format(sys.path))
 4 from a.Math_2 import Math_2
 5 #修改后
 6 from b.Math_4 import Math_4
 7 class Math_3:
 8 
 9     def __init__(self, a, b):
10         self.a = a
11         self.b = b
12         
13     def mul(self):
14         return self.a * self.b
15         
16     m2 = Math_2(3, 1)
17     print('the value of m2 is {}'.format(m2.sub()))
18     
19     m4 = Math_4(6, 2)
20     print('the value of m4 is {}'.format(m4.div()))
21         
22 if __name__ == '__main__':
23     m3 = Math_3(3, 2)
24     print('the value of m3 is {}'.format(m3.mul()))
知识兔

4、基于以上修改再次运行test_math.py文件，其结果如下

is ['D:\\PyEx\\math', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages']
the path of Math_3 is ['D:\\PyEx\\math', 'C:\\Python36\\python36.zip', 'C:\\Python36\\DLLs', 'C:\\Python36\\lib', 'C:\\Python36', 'C:\\Python36\\lib\\site-packages', '..']
the value of m2 is 2
the value of m4 is 3.0
the value of m1 is 3
the value of m3 is 20
知识兔
计算机