A module is a file that contains definitions—including variables and functions—that you can use once it is imported.There is a Python module named math that includes a number of useful variables and functions, and sqrt() is one of those functions. In order to access math, all you need is the import keyword. When you simply import a module this way, it's called a generic import.
Note: We have done this with randomand with datetime.
To import a function (in this case sqrt() function) from this module follow the steps:
import math .math. before sqrt() so that it has the form math.sqrt(). This tells Python not only to import math, but to get the sqrt() function from within math.Here you have an example:
>>> import math
>>> print math.sqrt(25)
5.0
It's possible to import only certain variables or functions from a given module. Pulling in just a single function from a module is called a function import, and it's done with the from keyword:
from module import function
For example:
>>> from math import sqrt
What if we still want all of the variables and functions in a module but don't want to have to constantly type math.?Universal import can handle this for you.
from module import *
Note:The *means all.
>>> from math import *
Universal imports may look great on the surface, but they're not a good idea for one very important reason: they fill your program with a ton of variable and function names without the safety of those names still being associated with the module(s) they came from. If you have a function of your very own named sqrt and you import math, your function is safe: there is your sqrt and there is math.sqrt. If you do from math import *, however, you have a problem: namely, two different functions with the exact same name.
Even if your own definitions don't directly conflict with names from imported modules, if you import * from several modules at once, you won't be able to figure out which variable or function came from where.
This code will show you everything available in the math module.
>>> import math # Imports the math module
>>> everything = dir(math) # Sets everything to a list of things from math
>>> print everything # Prints 'em all!
['__doc__', '__file__', '__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']
>>>
For these reasons, it's best to stick with either import module and type module.name or just import specific variables and functions from various modules as needed.