Functions

Defining

def func_id():
    suite

def func_id(param_list):
    suite

Calling

func_id()

func_id(param_list)

Arguments

• Parentheses are required, even when there are no parameters.
• Args are passed by value.
• Only args representing a mutable object can be modified (are inout parameters).

Argument types

id
id = default_value
*id                  A tuple of all remaining args (like C vararg).
**id                 A dictionary of all extra arguments passed as keywords.

Default arguments

• Default arg values are evaluated once, when the function is defined.

# Unintended behavior.
i = 5
def f(arg=i):
    print arg

i = 6
f() # will print 5

# Workaround solution, using None as the default value.
i = 5
def f(arg=None):
    if arg is None:
        arg=i
    print arg

i = 6
f() # will print 6

Keyword arguments

• Any keyword parameters used when calling a function must be after any positional parameters.

def test(param1, param2="beta", *rest, **keywords):
    print param1, param2

test("one", "two")
test("alpha")
test("un", param2="deux")

Return values

• A function can optionally return a value.
• Use a tuple to return more than one value.