python os.system执行cmd指令代码详解

# coding:utf-8
import os
os.system("ls")

def system(*args, **kwargs): # real signature unknown
  """ Execute the command in a subshell. """
  pass

(venv) C:\Users\TynamYang>python
Python 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:06:47) [MSC v.1914 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> import os
>>> cmd = 'echo "I am tynam"'
>>> os.system(cmd)
"I am tynam"
>>>

# Supply os.popen()
def popen(cmd, mode="r", buffering=-1):
  if not isinstance(cmd, str):
    raise TypeError("invalid cmd type (%s, expected string)" % type(cmd))
  if mode not in ("r", "w"):
    raise ValueError("invalid mode %r" % mode)
  if buffering == 0 or buffering is None:
    raise ValueError("popen() does not support unbuffered streams")
  import subprocess, io
  if mode == "r":
    proc = subprocess.Popen(cmd,
                shell=True,
                stdout=subprocess.PIPE,
                bufsize=buffering)
    return _wrap_close(io.TextIOWrapper(proc.stdout), proc)
  else:
    proc = subprocess.Popen(cmd,
                shell=True,
                stdin=subprocess.PIPE,
                bufsize=buffering)
    return _wrap_close(io.TextIOWrapper(proc.stdin), proc)

>>> import os
>>> cmd = 'echo "I am tynam"'
>>> f = os.popen(cmd, 'r')
>>> f.read()
'"I am tynam"\n'
>>>