Python Standard Library

The _ _builtin_ _ Module

This module contains built-in functions that are automatically available in all Python modules. You usually don’t have to import this module; Python does that for you when necessary.

Calling a Function with Arguments from a Tuple or Dictionary

Python allows you to build function argument lists on the fly. Just put all the arguments in a tuple, and call the built-in apply function, as illustrated in Example 1-1.

Example 1-1. Using the apply Function

File: builtin-apply-example-1.py

def function(a, b):
    print a, b

apply(function, ("whither", "canada?"))
apply(function, (1, 2 + 3))

whither canada?
1 5

To pass keyword arguments to a function, you can use a dictionary as the third argument to apply, as shown in Example 1-2.

Example 1-2. Using the apply Function to Pass Keyword Arguments

File: builtin-apply-example-2.py

def function(a, b):
    print a, b

apply(function, ("crunchy", "frog"))
apply(function, ("crunchy",), {"b": "frog"})
apply(function, (), {"a": "crunchy", "b": "frog"})

crunchy frog
crunchy frog
crunchy frog

One common use for apply is to pass constructor arguments from a subclass on to the base class, especially if the constructor takes a lot of arguments. See Example 1-3.

Example 1-3. Using the apply Function to Call Base Class Constructors

File: builtin-apply-example-3.py class Rectangle: def _ _init_ _(self, color="white", width=10, height=10): print "create a", color, self, "sized", width, "x", height class RoundedRectangle(Rectangle): def ...