Built in modules

A module is a file containing Python definitions and statements. Function is a piece of code which execute some logic.

>>> pow(2,3) #8

To check the built in function in python we can use dir(). If called without an argument, return the names in the current scope. Else, return an alphabetized list of names comprising (some of) the attribute of the given object, and of attributes reachable from it.

>>> dir(__builtins__)

[ 'ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '__debug__', '__doc__','__import__' , '__name__' , '__package__' , 'abs' , 'all' , 'any' , 'apply' , 'basestring' , 'bin' , 'bool' , 'buffer' , 'bytearray' , 'bytes' , 'callable' , 'chr' , 'classmethod' , 'cmp' , 'coerce' , 'compile' , 'complex' , 'copyright' , 'credits' , 'delattr' , 'dict' , 'dir' , 'divmod' , 'enumerate' , 'eval' , 'execfile' , 'exit' , 'file' , 'filter' , 'float' , 'format' , 'frozenset' , 'getattr' , 'globals' , 'hasattr' , 'hash' , 'help' , 'hex' , 'id' , 'input' , 'int' , 'intern' , 'isinstance' , 'issubclass' , 'iter' , 'len' , 'license' , 'list' , 'locals' , 'long' , 'map' , 'max' , 'memoryview' , 'min' , 'next' , 'object' , 'oct' , 'open' , 'ord' ,'pow', 'print', 'property', 'quit', 'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip' ]

To know the functionality of any function, we can use built in function help .

>>> help(max)
Help on built-in function max in module __builtin__:
max(...)
      max(iterable[, key=func]) -> value
      max(a, b, c, ...[, key=func]) -> value
      With a single iterable argument, return its largest item.
      With two or more arguments, return the largest argument.

Built in modules contains extra functionalities. For example to get square root of a number we need to include math module.

>>> import math
>>> math.sqrt(16) # 4.0

To know all the functions in a module we can assign the functions list to a variable, and then print the variable.

>>> import math
>>> dir(math)

['__doc__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc']

 it seems __doc__ is useful to provide some documentation in, say, functions

>>> math.__doc__

'This module is always available. It provides access to the\n mathematical functions defined by the C standard.'

import datetime

today = datetime.datetime.now()
str(today) # Output: '2016-09-15 06:58:46.915000'
repr(today) # Output: 'datetime.datetime(2016, 9, 15, 6, 58, 46, 915000)'