subprocess module of 12Python standard Library series

subprocess module of the Python standard library series

This module allows the spawn processes, connect to their input/output/error pipes, and obtain their return codes.

Examples of common methods

Call ()

Executes the command and returns the status code, indicating that the command 0 execution was successful, and that the command execution was unsuccessful.

>>> ret = Subprocess.call (["LS", "-l"], Shell=false) Total 4-rw-r--r--1 root root 172, 21:21 file.conf>& Gt;> ret0

Another way of doing it

# shell=true means call Native shell command to execute >>> ret = Subprocess.call ("Ls-l", Shell=true) Total 4-rw-r--r--1 root root 172 21:21 file.conf>>> Ret0

Check_call ()

Executes the command, returns 0 if the execution status code is 0, or throws an exception

# Execute a correct command will return execution result and status code >>> subprocess.check_call (["LS", "-l"]) total 4-rw-r--r--1 root root 172 may 21:21 file . conf0# If you are performing an incorrect command, you will be returned with an error message >>> subprocess.check_call (["LS", "a"]) Ls:cannot access a:no such file or dire Ctorytraceback (most recent): File ' <stdin> ', line 1, in <module> file "/usr/lib64/python2.6/subpr ocess.py ", line 505, in Check_call raise Calledprocesserror (Retcode, cmd) subprocess. Calledprocesserror:command ' [' ls ', ' a '] ' returned Non-zero exit status 2

Check_output ()

Executes the command, if the status code is 0, returns the execution result, otherwise throws an exception

# execution succeeds assigning the result of execution to the variable v>>> V = Subprocess.check_output ("Python-v", shell=true) # The command that executes the error will output an exception >>> Subprocess.check_output ("Pasas", shell=true) ' Pasas ' is not an internal or external command, nor is it a program or batch file that can be run.  Traceback (most recent): File ' <stdin> ', line 1, in <module> file ' C:\Python35\lib\subprocess.py ', Line 629, in Check_output **kwargs). StdOut File "C:\Python35\lib\subprocess.py", line 711, in run Output=stdout, s Tderr=stderr) subprocess. Calledprocesserror:command ' Pasas ' returned Non-zero exit status 1

The above three modes of execution, when executing the command,shellDefault equalsTrueEqualsTrue, the command inside the parentheses is a row, ifshellEqualsFalseSo[]The string inside is an element of the command, and when executed, the[]Strings inside the string are stitched together to execute.

Subprocess. Popen ()

call()、check_call()、check_output()The default internal calls aresubprocess.Popen(), whilesubprocess.Popen()is used to perform more complex system commands.

Parameters

Parameters	Description
Stdin	Standard input
StdOut	Standard output
StdErr	Error handle
Cwd	Used to set the current directory of the child process
Env	The environment variable used to specify the child process. If env = None, the environment variables of the child process are inherited from the parent process

Execute common commands

>>> subprocess. Popen ("Python-v", Shell=true) <subprocess. Popen object at 0x0000025c97233c88># python 3.5.1 is output result >>> python 3.5.1

There are two types of execution commands:

1. Input can be output, such as: ifconfig

2. Input for an interactive environment, relying on re-entry, such as: Python

>>> import subprocess# First go to the '/tmp ' directory and then create the subprocess folder, Shell=true >>> subprocess. Popen ("MkDir subprocess", shell=true, cwd= '/tmp ',) <subprocess. Popen object at 0x7f267cc3d390>>>> import os>>> os.system ("ls/tmp") subprocess

Subprocess. Popen () instance

# Importing Subprocess module import subprocess# Execute python command, enter Python interpreter, stdin standard input, stdout standard output, stderr error output, universal_newlines= True to automatically enter a newline character, obj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE, Universal_newlines=true) # Executes the standard input, the write is followed by the input command Obj.stdin.write ("print (1) \ n") Obj.stdin.write ("Print (2)") # After the input is turned off obj.stdin.close () # reads the contents of the standard output, assigns a value to the Cmd_out object cmd_out = Obj.stdout.read () # Turns off the standard output obj.stdout.close () # reads the contents of the error output, Assign to Cmd_error object cmd_error = Obj.stderr.read () # Turn off error Output obj.stderr.close () # Output content print (cmd_out) print (cmd_error)

Execution results

c:\python35\python.exe f:/python_code/sublime/week5/day02/sub.py12process finished with  Exit code 0 

# Importing Subprocess module import subprocess# Execute python command, enter Python interpreter, stdin standard input, stdout standard output, stderr error output, universal_newlines= True to automatically enter a newline character, obj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE, Universal_newlines=true) # executes two commands obj.stdin.write ("print (1) \ n") Obj.stdin.write ("Print (2)") # Communicate the error output or the content of the standard output to the Out_error_list object, if there is an error on the assignment error output, otherwise copy the standard output out_error_list = obj.communicate () # Output Out_ Content of the Error_list object print (out_error_list)

Execution results

c:\python35\python.exe f:/python_code/sublime/week5/day02/sub.py (' 1\n2\n ',  ') Process finished  with exit code 0 

# Importing Subprocess module import subprocess# Execute python command, enter Python interpreter, stdin standard input, stdout standard output, stderr error output, universal_newlines= True to automatically enter a newline character, obj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE, Universal_newlines=true) # Executes the print ("Hello") command directly, then assigns the error or the correct result to the Out_error_list object out_error_list = Obj.communicate (' Print (' "Hello ') ') # outputs the contents of the Out_error_list object print (out_error_list)

Execution results

C:\Python35\python.exe f:/python_code/sublime/week5/day02/sub.py (' hello\n ', ') Process finished with exit code 0

#Python标准库 #Subprocess

subprocess module of 12Python standard Library series