Basics Of Python Modules

A library refers to a collection of modules that together cater to a specific type of needs or application. Module is a file(.py file) containing variables, class definitions statements, and functions related to a particular task. Python modules that come preloaded with Python are called standard library modules.

Creating our module

We will be creating a module named tempConversion.py that converts values from F to C and vice-versa.

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# tempConversion.py to convert between
# between Fahrenheit and Centigrade
  
# function to convert F to C
def to_centigrade(x):
      return 5 * (x - 32) / 9.0
  
# function to convert C to F
def to_fahrenheit(x):
       return 9 * x / 5.0 + 32
  
# constants
  
# water freezing temperature(in Celcius)
FREEZING_C = 0.0  
  
# water freezing temperature(in Fahrenheit)     
FREEZING_F = 32.0      

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Now save this python file and the module is created. This module can be used in other programs after importing it.

Importing a module

In python, in order to use a module, it has to be imported. Python provides multiple ways to import modules in a program :

  1. To import the entire module :
    import module_name
  2. To import only a certain portion of the module :
    from module_name import object_name
  3. To import all the objects of the module :
    from module_name import *

Using an imported module

After importing the module, we can use any function/definition of the imported module as per the following syntax:



module_name.function_name() 

This way of referring to the module’s object is called dot notation.
If we import a function using from, there is no need to mention the module name and the dot notation to use that function.

Example 1 : Importing the whole module :

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# importing the module
import tempConversion
  
# using a function of the module
print(tempConversion.to_centigrade(12))
  
# fetching an object of the module
print(tempConversion.FREEZING_F)

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Output :

-11.11111111111111
32.0

Example 2 : Importing particular components of the module :

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# importing the to_fahrenheit() method
from tempConversion import to_fahrenheit
  
# using the imported method
print(to_fahrenheit(20))
  
# importing the FREEZING_C object
from tempConversion import FREEZING_C
  
# printing the imported variable
print(FREEZING_C)

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Output :

68.0
0.0

Python standard library functions

The python interpreter has a number of functions built into it that are always available. To use these built-in functions of python directly call the functions, like function_name(). Some built-in library functions are : input(), int(), float() etc

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num = 5
print("Number entered = ", num)
  
# oct() converts to octal number-string
onum = oct(num)   
  
# hex() coverts to hexadecimal number-string     
hnum = hex(num)     
     
print("Octal conversion yields", onum)
print("Hexadecimal conversion yields", hnum)
print(num)

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Output :

Number entered = 5
Octal conversion yields 0o5
Hexadecimal conversion yields 0x5
5



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