Argument passing

Arguments are passed by assigning local names to objects.

Strings and numbers are immutable objects. They cannot be changed from the function. Lists and dictionaries are mutable and can be changed.

#!/usr/bin/env python
def func( a, b):
    a = 1         # has only a local effect
    b[0] = 2      # changes the list in the calling function
    return

c = 3
d = [4, 5]
func( c, d)

print( " c ", c)
print( " d ", d)

Arguments may be collected in a list:

def scanFunc( *a):
    print( a)
    return

scanFunc( 1, 2, 3)

Arguments can be unpacked:

#!/usr/bin/env python

def func( a, b, c):
    print( a, b, c)
    return

a = [1, 2, 3]
func( *a)

Arguments may be collected in a dictionary:

#!/usr/bin/env python

def scanFunc( **a):
    print( a)
    return

scanFunc( start = 0,
          stop = 10,
          delta = 1)

Functions can have default values for arguments:

def yes_or_no(prompt, retries=4, complaint='Yes or no, please!'):
    while True:
        ok = raw_input(prompt)
        if ok in ('y', 'ye', 'yes'): return True
        if ok in ('n', 'no', 'nop', 'nope'): return False
        retries = retries - 1
        if retries < 0: raise IOError, 'refusenik user'
        print( complaint)

print( yes_or_no( "do you really want it "))

Here are examples for keyword arguments:

def scan( start, stop=100, delta=1):
    print( "scan from ", start, " to ", stop, "by ", delta)

scan( 10)                     # -> scan from  10  to  100 by  1
scan( 10, 200, 5)             # -> scan from  10  to  200 by  5
scan( 10, 200, delta=5)       # -> scan from  10  to  200 by  5
scan( 10, stop=200, delta=5)  # -> scan from  10  to  200 by  5

Receiving a list:

def func( *a):
    print( a)

func( 'a', 2, 3)

Receiving a dictionary:

def func( **a):
    print( a)

func( start= 0, stop= 10)

Collecting a list and a dictionary:

def scan( fname, *lst, **dct):
    print( fname, lst, dct)

scan( 'tst.fio', '1st comment', '2nd comment', start=0, stop=10, delta=1)

range() receives an unpacked list.

In [4]: a = [0,10]
In [5]: range(*a)
Out[5]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

func() receives an unpacked dictionary.

def func( name, start=0, stop=10):
    print( name, start, stop)

dct = {'name': 'tst', 'start': 1, 'stop': 2}
func( **dct)