A basic tutorial on arguments in python :)

argument_tutorial.py

line = '\n'+80*'*'+'\n' #formatting helper


# A quick overview of argument handling in python

# ************************************************************************
# In python, functions have arguments which are both positional and keyword
# arguments, that is you can call a function using implicit positions to assign
# values to an argument, or you can call them with specific arguments.
# Arguments can also have defaults in the function definition, as with the
# argument 'd' here, note that default arguments can only happen at the end
# after non-default arguments ie: def foo(a=1, b, c, d) is a syntax error:

def foo(a, b, c, d=4):
    print 'a', a
    print 'b', b
    print 'c', c
    print 'd', d

print line + "Regular arguments" + line

print "positional arguments with default"
foo(1, 2, 3)

print "\npositional arguments overriding default"
foo(2, 3, 4, 5)

# ************************************************************************
# Python has special syntax for dealing with arguments as lists and dicts,
# lists for positional arguments, dicts for keyword arguments. This syntax
# is * for positional arguments and ** for keyword arguments.

def bar(*positionalArguments, **keywordArguments):
    print 'positional', positionalArguments
    print 'keyword', keywordArguments

print line + "* and ** argument capturing" + line

print "\ncapturing only positional arguments"
bar(1,2,3,4)

print "\ncapturing only keyword arguments"
bar(a=1, b=2)

print "\ncapturing positional and keyword arguments"
bar(1, 2, c=3, d=4)


# ************************************************************************
# You can also mix these two techniques to capture some arguments explicitly,
# and others with * and **.

def baz(a, b=1, *positionalArguments, **keywordArguments):
    print 'a', a
    print 'b', b
    print 'positional', positionalArguments
    print 'keyword', keywordArguments

print line + "Mixing regular, * and ** argument capturing" + line

print "\nproviding only the minimum argument"
baz(1)

print "\nproviding a, b and some positional and keyword arguments"
baz(1, 2, 3, 4, 5, x="hello", y="world")

# Notice in the last instance, a and b do not get captured by the * and **.


# ************************************************************************
# Finally, the * and ** syntax serves a second purpse, when you call a function,
# you can use the same syntax to expand list and dict values into positional and
# keyword arguments. lets use the functions we've defined above and call them
# with some lists of values:

print line + "Using * and ** argument injection" + line

print "\nFilling all positional arguments from a list"
myArgs = ['I', '<3', 'skunks', '^_^']
foo(*myArgs)

print "\nFilling positional and keyword arguments from a list and a dict"
myArgs = ["hope", "you've", "found"]
myKWArgs = { 'this' : 'tutorial', 'kinda' : 'helpful!'}

bar(*myArgs, **myKWArgs)

# Ende~