平时写的每一个 py 文件都会 import 其他模块,但其原理我也是刚刚搞懂。
在使用 Python 的 import 导入模块时,会首先从缓存中检索 Python 内建的模块,比如 os、sys 等。
如果要使用的模块不是内建模块,之后会从指定的路径中依次查找。
sys.path 可以列出这些路径,它包含三部分内容:
- 当前 py 文件的目录;如果是在交互式环境,是当前终端的目录。
- 操作系统中的当前环境变量 PYTHONPATH 保存的所有路径
- 当前虚拟环境的路径,用来查找 pip 或 conda 安装的包。
~ % pwd
/Users/junsircoding
~ % ipython
In [1]: import sys
In [2]: sys.path
Out[2]:
['/Users/junsircoding/miniforge3/bin',
'/Users/junsircoding/miniforge3/lib/python39.zip',
'/Users/junsircoding/miniforge3/lib/python3.9',
'/Users/junsircoding/miniforge3/lib/python3.9/lib-dynload',
'',
'/Users/junsircoding/miniforge3/lib/python3.9/site-packages']
~ % python
>>> import sys
>>> import pprint as pp
>>> pp.pprint(sys.path)
['',
'/Users/junsircoding/miniforge3/lib/python39.zip',
'/Users/junsircoding/miniforge3/lib/python3.9',
'/Users/junsircoding/miniforge3/lib/python3.9/lib-dynload',
'/Users/junsircoding/miniforge3/lib/python3.9/site-packages']
>>> exit()
~ % export PYTHONPATH=/test/python_path
~ % ipython
In [1]: import sys
In [2]: sys.path
Out[2]:
['/Users/junsircoding/miniforge3/bin',
'/test/python_path',
'/Users/junsircoding/miniforge3/lib/python39.zip',
'/Users/junsircoding/miniforge3/lib/python3.9',
'/Users/junsircoding/miniforge3/lib/python3.9/lib-dynload',
'',
'/Users/junsircoding/miniforge3/lib/python3.9/site-packages']
~ % python
>>> import sys
>>> import pprint as pp
>>> pp.pprint(sys.path)
['',
'/test/python_path',
'/Users/junsircoding/miniforge3/lib/python39.zip',
'/Users/junsircoding/miniforge3/lib/python3.9',
'/Users/junsircoding/miniforge3/lib/python3.9/lib-dynload',
'/Users/junsircoding/miniforge3/lib/python3.9/site-packages']
>>> exit()