Python Utilities : 

We can do a number of things that we do in bash in unix , even in python interpreter .

one thing we have to do in 

import os 

now to see what are all the operations we can do  

EX_CANTCREAT

EX_CONFIG

EX_DATAERR

EX_IOERR

EX_NOHOST

EX_NOINPUT

EX_NOPERM

EX_NOUSER

EX_OK

EX_OSERR

EX_OSFILE

EX_PROTOCOL

EX_SOFTWARE

EX_TEMPFAIL

EX_UNAVAILABLE

EX_USAGE

F_OK

NGROUPS_MAX

O_APPEND

O_ASYNC

O_CREAT

O_DIRECT

O_DIRECTORY

O_DSYNC

O_EXCL

O_LARGEFILE

O_NDELAY

O_NOATIME

O_NOCTTY

O_NOFOLLOW

O_NONBLOCK

O_RDONLY

O_RDWR

O_RSYNC

O_SYNC

O_TRUNC

O_WRONLY

P_NOWAIT

P_NOWAITO

P_WAIT

R_OK

SEEK_CUR

SEEK_END

SEEK_SET

ST_APPEND

ST_MANDLOCK

ST_NOATIME

ST_NODEV

ST_NODIRATIME

ST_NOEXEC

ST_NOSUID

ST_RDONLY

ST_RELATIME

ST_SYNCHRONOUS

ST_WRITE

TMP_MAX

UserDict

WCONTINUED

WCOREDUMP

WEXITSTATUS

WIFCONTINUED

WIFEXITED

WIFSIGNALED

WIFSTOPPED

WNOHANG

WSTOPSIG

WTERMSIG

WUNTRACED

W_OK

X_OK

_Environ

__all__

__builtins__

__doc__

__file__

__name__

__package__

_copy_reg

_execvpe

_exists

_exit

_get_exports_list

_make_stat_result

_make_statvfs_result

_pickle_stat_result

_pickle_statvfs_result

_spawnvef

abort

access

altsep

chdir

chmod

chown

chroot

close

closerange

confstr

confstr_names

ctermid

curdir

defpath

devnull

dup

dup2

environ

errno

error

execl

execle

execlp

execlpe

execv

execve

execvp

execvpe

extsep

fchdir

fchmod

fchown

fdatasync

fdopen

fork

forkpty

fpathconf

fstat

fstatvfs

fsync

ftruncate

getcwd

getcwdu

getegid

getenv

geteuid

getgid

getgroups

getloadavg

getlogin

getpgid

getpgrp

getpid

getppid

getresgid

getresuid

getsid

getuid

initgroups

isatty

kill

killpg

lchown

linesep

link

listdir

lseek

lstat

major

makedev

makedirs

minor

mkdir

mkfifo

mknod

name

nice

open

openpty

pardir

path

pathconf

pathconf_names

pathsep

pipe

popen

popen2

popen3

popen4

putenv

read

readlink

remove

removedirs

rename

renames

rmdir

sep

setegid

seteuid

setgid

setgroups

setpgid

setpgrp

setregid

setresgid

setresuid

setreuid

setsid

setuid

spawnl

spawnle

spawnlp

spawnlpe

spawnv

spawnve

spawnvp

spawnvpe

stat

stat_float_times

stat_result

statvfs

statvfs_result

strerror

symlink

sys

sysconf

sysconf_names

system

tcgetpgrp

tcsetpgrp

tempnam

times

tmpfile

tmpnam

ttyname

umask

uname

unlink

unsetenv

urandom

utime

wait

wait3

wait4

waitpid

walk

write

Now we shall see some examples 

to list contents of dirctory 

os.listdir(directoryname)

list filenames in the directory 

os.path.exists( ) 

to see is the path exists

to do file copy 

import shutil

shutil.copy(source,dest) 

both strings source and dest denote filenames with path 

we cannot do it for copying entire folder content , this can be done by iterating over files inside the folder

Ok these are ways to simulate shell commands in python

Is there a way to run shell commands directly in python and show output 

Ya

import commands 

cmd = "ls -l ."

(status,output) = commands.getstatusoutput(cmd)

print output

this executes ls -l command on directory .  gives the output as a tuple having 2 things ., status (something like exit code, if 0 it means the command executed without error , if command execution had error it exits by sending 1 or even some other error code like 512 ) and the output of the command 

Interesting feature in python :

List comprehension 

if we have a list a = [1, 2 ,3,4]

then you want to get a new list which has the squares of these numbers ..

what we normally do is iterate through the list then get elements and then put it into the new list 

python has a easy way of doing this

b = [num*num      for num in a]

to put additional qualities like removing elements < 2 

b=[num*num     for num in a     if num>2]