A Python Application

• This is a python2 application.
• Last fall I gave an assignment where students were to write an assembly program to see if a number was prime.
• I needed to
  • Run the assembler on the program
    • If assembly failed, I needed to exit.
  • Test the program with a number different inputs
    • The program read from stdin
    • and wrote to stdout
• My solution used the subprocess libary
  • invokes a process like exec
  • But able to redirect i/o easily
  • This is a second generation library at least
    • It moves process execution to a higher level
  • Popen()
    • Takes a list of "command line arguments"
    • The first is the program to execute
    • Others are args

    • from subprocess import *
      Popen(["ls","-l"])
      

  • I/O redirection
    • stdin = , stdout=, stderr =
    • NONE, PIPE

    • a = Popen(["ls","-l"], stdout=PIPE)
      for line in a.stdout:
         print line
      

  • the shell= parameter
    • shell=False
      • The default
      • Disables things like globbing, pipes, wildcards, environment variables, ~ expansion, ...
      • The thing you should do for secure programs.
    • shell=True
      • Gives you the shell
      • And all of the tools
      • And no protection.
      • Uses /bin/sh

      • Popen(['/bin/sh', '-c', args[0], args[1], ...])
        

  • popen has many methods
• Have a look at this program