Python subprocess module details

subprocess

Subprocess:

One class Popen and others are wrapper over it. 
shell=True: This argument spawns a new intermediate process and run the command. If False, the command run in current process.

Popen: non blocking

subprcess call vs Popen:

call: is a wrapper over Popen and takes all the pamaters of popen. It is blocking and does not return until process has        finished.
    So, stdout=PIPE shall not be used with this becuase it keeps stdout in memeory till child process exit and child           process will hang as soon as it fills the OS pipe buffer.
    
Popen: Non-blocking. Can be made blocking with wait().
    wait():BLOCKING Waits for the child process to terminate and return returncode
    poll(): checks child process terminated? return returncode else None
    communicate():BLOCKING Iteract with the process. send data to stdin. Read data from stderr and stdout till the end of the file. Wait for the process to terminate. Returns a tuple (stdout, stderr)
    
    shell=True : Avoid shell=True by all means. Special chafracters must be escaped, allows user to run arbitrary programs                 on shell