Sixth day of the Python 11 issue

Common built-in modules

One, json/pickle string

1. JSON

Data exchange between different languages, and memory data exchange between different programs.

is similar to XML.

Import JSON

a={

' DB ': [1, ' Wang '],

' Home ': [' Zhang ', 45],

' Host ': {' name ': ' Ting ', ' age ': 24}

}

#将json写入文件

My_json=json.dumps (a)

F=file (' Data.txt ', ' WB ')

F.write (My_json)

#从文件中读取json

Af2=file (' data.txt ', ' RB ')

Af=af2.read ()

Json_data=json.loads (AF)

Af2.close ()

Dumps and loads are used in programs, dump and load can be written directly to the file, and loaded from the file.

2, Pickle

Import Pickle

a={

' DB ': [1, ' Wang '],

' Home ': [' Zhang ', 45],

' Host ': {' name ': ' Ting ', ' age ': 24}

}

#将字典数据pickle化写入文件

F=file (' Pickle1.txt ', ' W ')

Pickle.dump (A,F)

#从文件中读取pickle的数据:

F=file (' Pickle1.txt ', ' R ')

Pickle2=pickle.load (f)

print ' ===> ', pickle2

Pickle can serialize most of the python data structures, including time formats, classes, functions, and so on.

Note: When you pass files from Windows to Linux, that is, when you upload files across platforms, the official recommendation is ' RB ' or ' WB ' when you open files in Python. such as: File ('/tmp ', ' RB ')

Second, system-related modules

Execute system command:

Os.system () #只返回执行状态

os.spawn*

Os.popen () #可以返回执行结果, but will be discarded

The module that is about to be discarded (this module is not suitable for use on Windows, error):

Commands

Commands.getoutput (' dir ') #获取命令的结果

Commands.getstatus (' dir ') #获取命令的执行状态

Commands.getstatusoutput () #返回结果和状态

Third, subprocess

The above discarded modules are replaced by this module: subprocess

Subprocess.call ([' dir '],shell=true) #直接执行命令, no return result

#以下命令会把执行结果返回给变量

Cmd2=subprocess.check_output ([' dir '],shell=true)

Print CMD2

Check_call is thrown when a command executes an error, and when execution succeeds, it is the same as call.

Cmd2=subprocess.check_call ([' dir '],shell=true)

Popen similar to Os.popen:

Subprocess. Popen (...)

Used to perform complex system commands

Parameters:

The Args:shell command, which can be a string or sequence type (for example: list, tuple)

BufSize: Specifies buffering. 0 unbuffered, 1 row buffer, other buffer size, negative system buffering

stdin, stdout, stderr: Indicates the standard input, output, and error handles of the program, respectively

PREEXEC_FN: Valid only on UNIX platforms, specifying an executable object (callable object) that will be called before the child process is run

CLOSE_SFS: Under the Windows platform, if Close_fds is set to true, the newly created child process will not inherit the input, output, and error pipes of the parent process.

Therefore, you cannot set Close_fds to true while redirecting the standard input, output, and error (stdin, stdout, stderr) of the child process.

Shell: Ibid.

CWD: Used to set the current directory of child processes

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.

Universal_newlines: Different system line breaks differ, True----agree to use \ n

Startupinfo and Createionflags are only valid under Windows

will be passed to the underlying CreateProcess () function to set some properties of the child process, such as: the appearance of the main window, the priority of the process, etc.

Here are some examples:

Import subprocess

Ret1 = subprocess. Popen (["mkdir", "T1"])

Ret2 = subprocess. Popen ("mkdir T2", shell=true)

------------------------------------------------------------------------------

obj = subprocess. Popen ("mkdir T3", Shell=true, cwd= '/home/dev ',)

-------------------------------------------------------------------------------

Import subprocess

-----------------------------------------------------------------------------------------

obj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE)

Obj.stdin.write (' Print 1 \ n ')

Obj.stdin.write (' Print 2 \ n ')

Obj.stdin.write (' Print 3 \ n ')

Obj.stdin.write (' Print 4 \ n ')

Obj.stdin.close ()

Cmd_out = Obj.stdout.read ()

Obj.stdout.close ()

Cmd_error = Obj.stderr.read ()

Obj.stderr.close ()

Print Cmd_out

Print Cmd_error

--------------------------------------------------------------------------------

Import subprocess

obj = subprocess. Popen (["Python"], stdin=subprocess. PIPE, Stdout=subprocess. PIPE, Stderr=subprocess. PIPE)

Out_error_list = obj.communicate (' print ' hello ')

Print Out_error_list

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This article from "Linux World" blog, declined reprint!

Sixth day of the Python 11 issue