Using Python command line

Recently I had a task to write a command file for Windows that run a simple Python commands via python –c command. The manual says that command may contain multiple statements separated by newlines. Unfortunately, Windows console doesn’t allow it (and Ctrl-T trick doesn’t help) so I had to find a workaround. The intuition and language reference helped me to find out that the simple statements can be separated by semicolons like in C/C++ (however, these languages allow to separate all the commands, not
the only simple ones).

Let me give an example. Imagine that accidentally I want to know the error message corresponding to the error code 9. Of course, I can read manuals and documentation, but there is a more simple way:

$ python -c "import os;print os.strerror(9)"
Bad file descriptor

But this "trick" works only with simple statements. It is not allowed to mix simple and compound statements, so the following command will not work: python -c "import os;for i in range(42):print i,os.strerror(i)". The only way to make it workable – put compound statement on the upper level (identical imports doesn't matter, the real import will be executed only once):

$ python -c "for i in range(43):import os;print i,os.strerror(i)"
0 No error
1 Operation not permitted
2 No such file or directory
3 No such process
4 Interrupted function call
5 Input/output error
6 No such device or address
7 Arg list too long
8 Exec format error
9 Bad file descriptor
10 No child processes
11 Resource temporarily unavailable
12 Not enough space
13 Permission denied
14 Bad address
15 Unknown error
16 Resource device
17 File exists
18 Improper link
19 No such device
20 Not a directory
21 Is a directory
22 Invalid argument
23 Too many open files in system
24 Too many open files
25 Inappropriate I/O control operation
26 Unknown error
27 File too large
28 No space left on device
29 Invalid seek
30 Read-only file system
31 Too many links
32 Broken pipe
33 Domain error
34 Result too large
35 Unknown error
36 Resource deadlock avoided
37 Unknown error
38 Filename too long
39 No locks available
40 Function not implemented
41 Directory not empty
42 Illegal byte sequence 

Also I want to notice one more feature of Python command line – executing modules content. Python contains many useful modules and some of them are more useful than
someone can think – they can be executed. For example, SimpleHTTPServer allows you to share your current directory information and files via HTTP protocol:

$ python -m SimpleHTTPServer
Serving HTTP on 0.0.0.0 port 8000 ... 

I’ve gathered information about executable modules and want to share it with you:

CommandFunctionality
python -m sitePrint some useful information (sys.path, USER_BASE, USER_SITE)
python -m StringIORead information about the file (default: /etc/passwd)
python -m calendarShow the console calendar
python -m zipfileZip/unzip analogue
python -m platformPrint the platform information
python -m mailcapShow and execute MIME types handlers
python -m binhexConvert the binary file to hex
python -m sgmllibParse the html file
python -m htmllibShow the html file in the text mode
python -m webbrowserStart the default web browser for the required URL
python -m urllibPrint the content of the remote site
python -m ftplibSimple FTP client
python -m poplibPrint information about the remote mailbox
python -m smtpdRFC 2821 SMTP proxy
python -m telnetlibSimple telnet client
python -m SimpleHTTPServerSimple HTTP server
python -m CGIHTTPServerCGI-savvy HTTP server
python -m aifcPrint information about the .aiff file
python -m sndhdrPrint information about sound files
python -m localePrint locale information
python -m shlexSplit the file to tokens
python -m pydocPython documentation tool
python -m doctestDoctest runner
python -m unittestUnittest runner
python -m pdbPython debugger
python -m timeitTool for measuring execution time of small code snippets
python -m traceTrace Python program or function execution
python -m codePython interpreter emulator
python -m tokenizeSplit the file to tokens with detailed information
python -m pyclbrDescribe Python module classes and methods
python -m compileallCompile all .py files to .pyc (.pyo) files
python -m filecmpCompare two directory
python -m gzipGzip/gunzip analogue
python -m base64RFC 3548: Base16, Base32, Base64 data encoder
python -m quopriConvert to/from quoted-printable transport encoding as per RFC 1521
python -m cProfileProfile Python code via 'lsprof' profiler
python -m profileProfile Python code
python -m uuImplement UUencode and UUdecode functions
python -m disDisassemble of Python byte code into mnemonics
python -m formatterGeneric output formatter

Most useful modules will be described in my next article. Enjoy!

Comments

  1. Hi!
    Nice and useful post, though I've got the following import error:

    viktor@viktor-laptop:~$ python -m pydoc -p 8800

    Traceback (most recent call last):
    File "/usr/lib/python2.6/runpy.py", line 122, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
    File "/usr/lib/python2.6/runpy.py", line 34, in _run_code
    exec code in run_globals
    File "/usr/lib/python2.6/pydoc.py", line 2340, in
    if __name__ == '__main__': cli()
    File "/usr/lib/python2.6/pydoc.py", line 2290, in cli
    serve(port, ready, stopped)
    File "/usr/lib/python2.6/pydoc.py", line 1979, in serve
    import BaseHTTPServer, mimetools, select
    ImportError: No module named BaseHTTPServer

    However, it doesn't occur when i'm using this code:

    viktor@viktor-laptop:~$ python -c "import pydoc; pydoc.cli()" -p 8800
    pydoc server ready at http://localhost:8800/

    What do you think about it?
    (I'm using python2.6 on ubuntu 9.04)

    Thanks in advance.

    ReplyDelete
  2. "-m" option terminates the option list, so you can't pass "-p" option for pydoc module (or at least it doesn't work as intended to work):

    $ python -h | grep "^\-m"
    -m mod : run library module as a script (terminates option list)

    However, there is pydoc script in the /usr/bin directory that exactly resemble the code you mentioned:

    $ cat /usr/bin/pydoc
    #! /usr/bin/python2.6

    import pydoc
    if __name__ == '__main__':
    pydoc.cli()

    So you can just call pydoc script with the all required options and enjoy Python documentation:

    $ pydoc -p 8800
    pydoc server ready at http://localhost:8800/

    So, the "-m" option is not so useful as can be, but you can always emulate its behavior. First, you need to know the module path. You can do it like this:

    $ python -c "import pydoc;print pydoc"
    <module 'pydoc' from '/usr/lib/python2.6/pydoc.pyc'>

    And then just start the required script:

    $ python /usr/lib/python2.6/pydoc.pyc -p 8800
    pydoc server ready at http://localhost:8800/

    Hope it helps, if you have further questions or suggestions let me know. Good luck!

    ReplyDelete

Post a Comment

Popular posts from this blog

DIY: Business cards in LaTeX

Python vs JS vs PHP for embedded systems

Shellcode detection using libemu