一句python代码引发的学习(菜鸟版)

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xjgwwwnd 2024-03-24 14:08:13 博主文章分类：python ©著作权

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一句python代码


sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__)),
                                'lib'))

代码分析

本意是在sys.path列表中增加搜索.py文件的路径

这个路径是执行这个python代码的文件的目录的目录(比较拗口哦)，如file的路径在/home/gwang/python/file，那么sys.path中就会增加/home/gwang/lib

比如一下代码(python_ospath.py):

import os
import sys

print(sys.path)
sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__)),'lib'))
print(sys.path)

结果如下:

~/gwang/python$ python python_ospath.py
['/home/gwang/python', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages']
['/home/gwang/lib', '/home/gwang/python', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages']

~/gwang$ python python/python_ospath.py
['/home/gwang/python', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages']
['/home/gwang/lib', '/home/gwang/python', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages']

sys.path路径中增加了'/home/gwang/lib'，实际文件路径'/home/gwang/python/python_ospath.py'，不过还可以看到sys.path也增加了执行文件的目录'/home/gwang/python/’

sys.path.insert

$ python
...
>>> import sys
>>> help(sys)
......
path -- module search path; path[0] is the script directory, else ''
>>> help(sys.path)
 insert(self, index, object, /)
 |      Insert object before index.

sys.path 是指定模块搜索路径的字符串列表，可以使用print()函数查看，sys.path添加路径后，可以从添加的路径导入模块

还可以参考: sys.path.append

os.path.join

$ python
...
>>> import os
>>> help(os.path)
...
join(a, *p)
        Join two or more pathname components, inserting '/' as needed.
        If any component is an absolute path, all previous path components
        will be discarded.  An empty last part will result in a path that
        ends with a separator.
        连接两个或多个路径名组件，根据需要插入“/”。
         如果任何组件是绝对路径，则所有先前的路径组件将被丢弃。 
         最后一部分为空将导致路径以分隔符结尾。

os.path.join的示例代码(path_join.py)

import os

root="/"
a="a"
b="b"
c="/c"
d="d"
e="e.txt"

f=a+b+c+d+e

print(os.path.join(root,f))
print(os.path.join(root,a,b,c))
print(os.path.join(root,a,c,d,e))
print(os.path.join(root,a,d,e))
print(os.path.join(root,a,d,e,c))

说明:c路径比较特殊是绝对路径，所以前面的路径组件都会被丢弃，比如root,a,d,e,c的组合不是/a/d/e.txt//c而是直接为/c

输出结果如下:

$ python path_join.py
/ab/cde.txt
/c
/c/d/e.txt
/a/d/e.txt
/c

os.path.dirname

$ python
...
>>> import os
>>> help(os.path)
...
 dirname(p)
        Returns the directory component of a pathname
        返回路径名的目录部分

示例代码

import os
import sys

if len(sys.argv) > 1:
    print("dirname=", os.path.dirname(str(sys.argv[1])))
    print("dirofdir=", os.path.dirname(os.path.dirname(str(sys.argv[1]))))

输出结果如下:

$ python python_dirname.py /123/d/
dirname= /123/d
dirofdir= /123
$ python python_dirname.py file.xt
dirname=
dirofdir=
$ python python_dirname.py /456/a/b/cfile.xt
dirname= /456/a/b
dirofdir= /456/a
$ python python_dirname.py /
dirname= /
dirofdir= /
$ python python_dirname.py .
dirname=
dirofdir=