Core Python Programming (2nd Edition)

In addition, because of the unification of types and classes in Python 2.2, all of these built-in functions
were converted into factory functions. Factory functions, introduced in Chapter 4, just means that these
objects are now classes, and when you "call" them, you are just creating an instance of that class.
They will still behave in a similar way to the new Python user so it is probably something you do not
have to worry about.
The following are some examples of using these functions:
>>> int(4.25555)
4
>>> long(42)
42L
>>> float(4)
4.0
>>> complex(4)
(4+0j)
>>>
>>> complex(2.4, -8)
(2.4-8j)
>>>
>>> complex(2.3e-10, 45.3e4)
(2.3e-10+453000j)
Table 5.5 summarizes the numeric type factory functions.
Table 5.5. Numeric Type Factory Functions [a]
Class (Factory Function) Operation
[b] Returns the Boolean value of obj, e.g., the value of
bool(obj)
executing obj.__nonzero__()
int(obj, base=10) Returns integer representation of string or number obj;
similar to string.atoi(); optional base argument
introduced in 1.6
long(obj, base=10) Returns long representation of string or number obj;
similar to string.atol(); optional base argument
introduced in 1.6
float(obj) Returns floating point representation of string or number
obj; similar to string.atof()
complex(str) or complex(real, imag=0.0) Returns complex number representation of str, or builds
one given real (and perhaps imaginary) component(s)
[a] Prior to Python 2.3, these were all built-in functions.