A built-in function object is a wrapper around a C function. Examples of built-in functions are len and math.sin() (math is a standard built-in module). The number and type of the arguments are determined by the C function.
Special read-only attributes:
- __doc__ is the function’s documentation string, or None if unavailable.
- __name__ is the function’s name
- __self__ is set to None (but see the next section)
- __module__ is the name of the module the function was defined in or None if unavailable.
This is really a different disguise of a built-in function, this time
containing an object passed to the C function as an implicit extra
argument. An example of a built-in method is
assuming alist is a list object. In this case, the special read-only
attribute __self__ is set to the object denoted by list.