• 1. 没有安装
  • 1.1. python mytree
  • 1.2. python -m mytree
• 2. 已安装

---

加入了__main__.py 后，我们就可以直接执行包名。python -m mytree 和 python mytree。

其实执行都是 mytree/__main__.py。

qqq
├── mytree
│   ├── __main__.py
│   ├── tree.py

# __main__.py

import os
print('[__name__]', __name__)
print('[__package__]', __package__)
print('[file position]', (os.path.abspath(__file__)))
print("[I am being accessed from]", os.path.abspath(os.curdir))

# from .tree import main
# main()

import mytree.tree as tree
tree.main()

# import tree
# tree.main()

1. 没有安装

1.1. python mytree

• [ ] __name__是__main__ 失效:
• [ ] 不知道 __package__
• [x] 将包含__main__.py的目录mytree加入到 search path sys.path 中

特性1和2都不满足，所以不能使用相对导入:

# from .tree import main
# ImportError: attempted relative import with no known parent package

# import mytree.tree as tree
# ModuleNotFoundError: No module named 'mytree'

import tree   # 因为特性3

# from .tree import main
qqq $ python mytree
[__name__] __main__
[__package__]
[file position] D:\git\localToolkit\linux_scripts\qqq\mytree\__main__.py
[I am being accessed from] D:\git\localToolkit\linux_scripts\qqq
Traceback (most recent call last):
  File "D:\miniconda\envs\ldm\lib\runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "D:\miniconda\envs\ldm\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "D:\git\localToolkit\linux_scripts\qqq\mytree\__main__.py", line 7, in <module>
    from .tree import main
ImportError: attempted relative import with no known parent package

特性3满足，所以执行路径哪都行：

# import tree   # 在mytree之外的路径也可以。
linux_scripts $ python qqq/mytree
[__name__] __main__
[__package__]
[file position] D:\git\localToolkit\linux_scripts\qqq\mytree\__main__.py
[I am being accessed from] D:\git\localToolkit\linux_scripts

1.2. python -m mytree

• [ ] __name__是__main__ 失效
• [x] 知道 __package__
• [ ] 不会将包含__main__.py的目录mytree加入到 search path sys.path 中

特性1和2中其一满足，所以能使用相对导入:

from .tree import main

import mytree.tree as tree

# import tree
# ModuleNotFoundError: No module named 'mytree'

特性3不满足，所以只能在 mytree 的父目录下执行：

# import tree 
qqq $ python -m mytree
[__name__] __main__
[__package__] mytree
[file position] D:\git\localToolkit\linux_scripts\qqq\mytree\__main__.py
[I am being accessed from] D:\git\localToolkit\linux_scripts\qqq
Traceback (most recent call last):
  File "D:\miniconda\envs\ldm\lib\runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "D:\miniconda\envs\ldm\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "D:\git\localToolkit\linux_scripts\qqq\mytree\__main__.py", line 8, in <module>
    import tree as tree
ModuleNotFoundError: No module named 'tree'

2. 已安装

还是 python -m mytree 的情况。但是由于已安装到site-packages中，所以 search path 是找得到的，就不局限于执行的工作路径。

另外，还有一种情况支持import mytree————切换到包的目录下。因为"PYTHONPATH: 默认值是当前工作目录 working directory"，所以能找到。

# pip install . 不行,找不到
# 因为development安装，下面进入到mytree文件夹下才行。
$ pip install -e .

# import mytree
mytree $python -m mytree  
[__name__] __main__
[__package__] mytree
[file position] d:\git\localtoolkit\linux_scripts\qqq\mytree\__main__.py
[I am being accessed from] D:\git\localToolkit\linux_scripts\qqq\mytree