21. python -m

Python 加载 py 文件的方式：

  • python xxx.py ：以直接运行的方式启动。

  • python -m xxx ：以模块的方式启动。

执行 python -h 可以找到：

-m mod : run library module as a script (terminates option list)

21.1. 两种方式的异同

新建 run.py 如下:

a/
└── run.py

1import sys
2
3print(sys.path)
4
5print(__name__)
6
7if __name__ == "__main__":
8    print("Directly launched.")

执行 python a/run.py:

['/data6/fong/a', '/home/fong/anaconda3/envs/python37/lib/python37.zip', '/home/fong/anaconda3/envs/python37/lib/python3.7', '/home/fong/anaconda3/envs/python37/lib/python3.7/lib-dynload', '/home/fong/.local/lib/python3.7/site-packages', '/home/fong/anaconda3/envs/python37/lib/python3.7/site-packages']
__main__
Directly launched.

执行 python -m a/run （Python3 执行 python -m a.run ）:

['/data6/fong', '/home/fong/anaconda3/envs/python37/lib/python37.zip', '/home/fong/anaconda3/envs/python37/lib/python3.7', '/home/fong/anaconda3/envs/python37/lib/python3.7/lib-dynload', '/home/fong/.local/lib/python3.7/site-packages', '/home/fong/anaconda3/envs/python37/lib/python3.7/site-packages']
__main__
Directly launched.

对比可以发现：

  • 两者都会把定位到的模块脚本当成 主程序 入口来执行，执行时该脚本的 __name__ 都是 __main__ 。

  • sys.path[0] 是不一样的，一个是脚本所在目录，另一个是执行命令所在的目录。

Note

python -m run 会从 sys.path 查找模块 run ，如果把 run 的路径放入 sys.path 中，则执行的时候不需要再指定路径。

21.2. 示例

新建目录如下:

.
├── pkg1
│   ├── __init__.py
│   └── my_module.py
└── pkg2
    ├── __init__.py
    └── run.py

run.py 内容如下:

import sys
print(sys.path)

from pkg1 import my_module

执行 python pkg2/run.py:

['/data6/fong/a/test/pkg2', '/home/fong/anaconda3/envs/python37/lib/python37.zip', '/home/fong/anaconda3/envs/python37/lib/python3.7', '/home/fong/anaconda3/envs/python37/lib/python3.7/lib-dynload', '/home/fong/.local/lib/python3.7/site-packages', '/home/fong/anaconda3/envs/python37/lib/python3.7/site-packages']
Traceback (most recent call last):
File "pkg2/run.py", line 4, in <module>
    from pkg1 import my_module
ModuleNotFoundError: No module named 'pkg1'

执行 python -m pkg2/run:

['/data6/fong/a/test', '/home/fong/anaconda3/envs/python37/lib/python37.zip', '/home/fong/anaconda3/envs/python37/lib/python3.7', '/home/fong/anaconda3/envs/python37/lib/python3.7/lib-dynload', '/home/fong/.local/lib/python3.7/site-packages', '/home/fong/anaconda3/envs/python37/lib/python3.7/site-packages']

21.3. 参考资料

  1. Python 中 -m 的典型用法、原理解析与发展演变