Open a text editor, e.g. !emacs first_script.py:
================================================
#This is a comment

# a python command
print "This is my first script!"

# a call to a system/shell command
os.system('rm -rf myscript.listobs')

# a CASA command [see  inp listobs for parameters]
listobs(vis='<yourvis>',listfile='myscript.listobs')


=> in CASA: execfile('first_script.py')