Python Modules

Python Modules#

Learn to create and import custom modules in Python. Also, you will find different techniques to import and use custom and built-in modules in Python.

What are modules in Python?#

Module containing a set of codes or a set of functions which can be included to an application. Modules refer to the Python file, which contains Python code like Python statements, classes, functions, variables, etc. A file with Python code is defined with extension**.py**

For example: In main.py, where the main is the module name.

In Python, large code is divided into small modules. The benefit of modules is, it provides a way to share reusable functions.

Advantage#

Reusability: Module can be used in some other python code. Hence it provides the facility of code reusability.
Categorization: Similar type of attributes can be placed in one module.

Creating a module in Python#

A file containing Python code, for example: example.py, is called a module, and its module name would be example.

We use modules to break down large programs into small manageable and organized files. Furthermore, modules provide reusability of code.

We can define our most used functions in a module and import it, instead of copying their definitions into different programs.

The module contains Python code like classes, functions, methods, but it also has variables. A variable can list, tuple, dict, etc.

Let us create a module. Type the following and save it as example.py.

# Python Module example

>>> def add(a, b):
>>>     """This program adds two numbers and return the result"""
>>>     result = a + b
>>>     return result

Here, we have defined a function add() inside a module named example. The function takes in two numbers and returns their sum.

How to import modules in Python?#

We can import the definitions inside a module to another module or the interactive interpreter in Python.

We use the import keyword to do this. To import our previously defined module example, we type the following in the Python prompt.

>>> import example

This does not import the names of the functions defined in example directly in the current symbol table. It only imports the module name example there.

Using the module name we can access the function using the dot . operator. For example:

# Example 1:

import example
example.add(3,6.6)

9.6

Python has tons of standard modules. You can check out the full list of Python standard modules and their use cases. These files are in the Lib directory inside the location where you installed Python.

Standard modules can be imported the same way as we import our user-defined modules.

There are various ways to import modules. They are listed below:

** # Example 2:**

The Python code for a module named a name normally resides in a file main.py. But first create a function in test.py. Here is an example of a simple module,

test.py -

>>> def fun():
>>>     print("something here inside fun()")

main.py −

>>> import test
>>> from test import fun
>>> fun()

Output of above example: Run main.py

something here inside fun()

For test.ipynb or test1.ipynb and main.ipynb

Open anaconda prompt and type pip install import-ipynb

see: Downloading import-ipynb-0.1.3.tar.gz (4.0 kB)

test.py or test1.ipynb -

>>> def fun():
>>>     print("something here inside fun()")

main.ipynb −

>>> import import_ipynb

>>> import test1
>>> from test1 import fun
>>> fun()

Output of above example: Run main.ipynb

something here inside fun()

# Example 3:

fibo.py -

# Fibonacci numbers module
>>> def fib(n): # return Fibonacci series up to n
>>>     result = []
>>>     a, b = 0, 1
>>>     while b < n:
>>>         result.append(b)
>>>         a, b = b, a + b
>>>     return result

main.py −

>>> import fibo
>>> from fibo import fib
>>> print(fib(100))

Output of above example: Run main.py

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

For test.ipynb or test1.ipynb and main.ipynb

Open anaconda prompt and type pip install import-ipynb

see: Downloading import-ipynb-0.1.3.tar.gz (4.0 kB)

fibo1.ipynb or fibo.py -

# Fibonacci numbers module
>>> def fib(n): # return Fibonacci series up to n
>>>     result = []
>>>     a, b = 0, 1
>>>     while b < n:
>>>         result.append(b)
>>>         a, b = b, a + b
>>>     return result

main.ipynb −

>>> import import_ipynb

>>> import fibo1
>>> from fibo1 import fib
>>> print(fib(100))

Output of above example: Run main.ipynb

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

# Example 4:

equal.py -

#function definition
>>> def equal(a, b):
>>>     if(a == b):
>>>         return True

main.py −

>>> from equal import *
>>> a, b = 10, 10
>>> print(equal(a, b))

Output of above example: Run main.py

True

For equal.ipynb or equal1.ipynb and main.ipynb

Open anaconda prompt and type pip install import-ipynb

see: Downloading import-ipynb-0.1.3.tar.gz (4.0 kB)

equal.ipynb or equal1.ipynb -

#function definition
>>> def equal(a, b):
>>>     if(a == b):
>>>         return True

main.ipynb −

>>> import import_ipynb

>>> from equal1 import *
>>> a, b = 10, 10
>>> print(equal(a, b))

Output of above example: Run main.ipynb

True

In Python, each and every built-in module has a large number of predefined functions to perform specific tasks. For instance, Python has a built-in module named operator, inside which the function called eq() is defined. This function returns the boolean value of True if the given two input values are equal. Else, returns False.

So now, we can make use of this operator module in our main() program to check if two numbers are equal. This means we would no longer need that equal.py module.

# Example 5: 

#main function
from operator import *
a, b = 10, 10
print(eq(a, b))

True

Python `import` statement#

We can import a module using the import statement and access the definitions inside it using the dot operator . as described above. Here is an example.

# Example 1: 

# import statement example to import standard module math
import math
print("The value of pi is", math.pi)

The value of pi is 3.141592653589793

# Example 2:

import math

# use math module functions
print(math.sqrt(6))    # Output 2.449489742783178

2.449489742783178

`import` multiple modules#

If we want to use more than one module, then we can import multiple modules. This is the simplest form of import a keyword that we already use in the above example.

# Example 1: Import two modules

import math, random

print(math.factorial(6))
print(random.randint(10, 30))

720
28

Python `from-import` statement#

To import particular classes or functions, we can use the from-import statement. It is an alternate way to import. By using this form, we can import individual attributes and methods directly into the program.We can import specific names from a module without importing the module as a whole.

# Example 1: import only factorial function from math module
from math import factorial

print(factorial(6))

# Example 2: 

from math import pi, e
e

2.718281828459045

# Example 3: 

# import only pi from math module
from math import pi
print("The value of pi is", pi)

The value of pi is 3.141592653589793

Here, we imported only the pi attribute from the math module.

In such cases, we don’t use the dot operator. We can also import multiple attributes as follows:

# Example 4: 

from math import pi, e
pi

3.141592653589793

`import` with renaming#

We can import a module by renaming it as follows:

# Example 1: 

# import module by renaming it
import math as m
print("The value of pi is", m.pi)

The value of pi is 3.141592653589793

We have renamed the math module as m. This can save us typing time in some cases.

Note: that the name math is not recognized in our scope. Hence, math.pi is invalid, and m.pi is the correct implementation.

# Example 2:  Import a module by renaming it

import random as rand

print(rand.randrange(10, 20, 2))

# Example 3:  import a method by renaming it

# rename randint as random_number
from random import randint as random_number

# Gives any random number from range(10, 50)
print(random_number(30, 60))

`import` all names#

We can import all functions and attributes of a specific module, then instead of writing all function names and attribute names, we can import all using an asterisk *.

# Example 1: 

# import all names from the standard module math

from math import *
print("The value of pi is", pi)

The value of pi is 3.141592653589793

Here, we have imported all the definitions from the math module. This includes all names visible in our scope except those beginning with an underscore(private definitions).

Importing everything with the asterisk * symbol is not a good programming practice. This can lead to duplicate definitions for an identifier. It also hampers the readability of our code.

# Example 2: 

from math import *
print(pow(6,3))
print(factorial(6))

print(pi*3)
print(sqrt(100))

0
720
42477796076938
0

Python Module Search Path#

While importing a module, Python looks at several places. Interpreter first looks for a built-in module. Then(if built-in module not found), Python looks into a list of directories defined in sys.path. The search is in this order.

The current directory.
PYTHONPATH (an environment variable with a list of directories).
The installation-dependent default directory.

import sys
sys.path

['C:\\Users\\Deepak\\01_Learn_Python4Data\\04_Python_Functions',
 'C:\\ProgramData\\Anaconda3\\python38.zip',
 'C:\\ProgramData\\Anaconda3\\DLLs',
 'C:\\ProgramData\\Anaconda3\\lib',
 'C:\\ProgramData\\Anaconda3',
 '',
 'C:\\Users\\Deepak\\AppData\\Roaming\\Python\\Python38\\site-packages',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\locket-0.2.1-py3.8.egg',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32\\lib',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\Pythonwin',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\IPython\\extensions',
 'C:\\Users\\Deepak\\.ipython']

We can add and modify this list to add our own path.

Reloading a module#

The Python interpreter imports a module only once during a session. This makes things more efficient. Foe example:

# Example 1:

Suppose we have the following code in a module named my_module.

# This module shows the effect of
#  multiple imports and reload

print("This code got executed")

import my_module

This code got executed

We can see that our code got executed only once. This goes to say that our module was imported only once.

Now if our module changed during the course of the program, we would have to reload it.One way to do this is to restart the interpreter. But this does not help much.

Python provides a more efficient way of doing this. We can use the reload() function inside the imp module to reload a module. We can do it in the following ways:

import imp
import my_module

import my_module
imp.reload(my_module)

This code got executed

<module 'my_module' from 'C:\\Users\\Deepak\\01_Learn_Python4Data\\04_Python_Functions\\my_module.py'>

# Example 2:

First, create a Python module with the name greet_module.pynb and write the below code in that file.

>>> print("Welcome to Dr Parmar's Python4DataScience class")

Now, create a Python file with the name, main.py and write the below code in it and import the module test_module.py. See the following code.

>>> import import_ipynb
>>> import time
>>> from importlib import reload

>>> # load 1st time
>>> import test_module
>>> time.sleep(25)
>>> # reload 
>>> reload(test_module)
>>> time.sleep(25) 

>>> # reload again  
>>> reload(test_module)
>>> print("This is test file..")

Output of above example: Run main.py

Welcome to Dr Parmar's Python4DataScience class
Welcome to Dr Parmar's Python4DataScience class
Welcome to Dr Parmar's Python4DataScience class
This is test file..

The `dir()` built-in function#

We can use the dir() function to find out names that are defined inside a module. When we use this function with any object (an object can be sequence like list, tuple, set, dict or can be class, function, module, etc. ), it returns properties, attributes, and method.

For example, we have defined a function add() in the module example that we had in the beginning.

We can use dir in example module in the following way:

# Example 1:

dir(example)

['__builtins__',
 '__cached__',
 '__doc__',
 '__file__',
 '__loader__',
 '__name__',
 '__package__',
 '__spec__',
 'add']

Here, we can see a sorted list of names (along with add). All other names that begin with an underscore are default Python attributes associated with the module (not user-defined).

For example, the __name__ attribute contains the name of the module.

# Example 2:

import example
example.__name__

'example'

All the names defined in our current namespace can be found out using the dir() function without any arguments.

# Example 3:

a = 1
b = "hello"
import math
dir()
['__builtins__', '__doc__', '__name__', 'a', 'b', 'math', 'pyscripter']

['__builtins__', '__doc__', '__name__', 'a', 'b', 'math', 'pyscripter']

# Example 4:

import math

print(dir(math))

['__doc__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'comb', 'copysign', 'cos', 'cosh', 'degrees', 'dist', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 'isqrt', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'perm', 'pi', 'pow', 'prod', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc']

Python Modules List#

Using Python built-in function help(), we can obtain the list of built-in modules available in Python. On executing the line help (‘modules’) in Python IDE, you can see all the Python built-in modules. Some of the frequently used ones are discussed below.

Module	Description
`Operator`	This module provides a set of pre-defined functions corresponding to operators in Python.
`decimal`	This module is used to print the complete decimal value when one number is divided by another number.
random	random module is used to generate random numbers. Some of the pre-defined functions of this module are `randint()`, `choice()`, `uniform`, etc.
`string`	string module provides a set of functions that are used to perform certain operations on characters. This module has pre-defined functions like capwords, ascii_letters, etc.
math	math module is used to perform mathematical operations. This module provides some pre-defined mathematical functions like sqrt, factorial, etc.

Python Built-In Modules Examples#

There are many built-in modules in Python. Some of the common built-in modules: os, sys, operator, string, decimal, random , math, statistics, datetime, time, collections, threading, mailbox, tkinter, json, re, etc.

Example Using `os` Module#

Using python os module it is possible to automatically perform many operating system tasks. The os module in Python provides functions for creating, changing current working directory, and removing a directory (folder), fetching its contents, changing and identifying the current directory.

# Example 1:

# import the module
import os
# Creating a directory
os.mkdir('directory_name')
# Changing the current directory
os.chdir('path')
# Getting current working directory
os.getcwd()
# Removing directory
os.rmdir()

---------------------------------------------------------------------------
FileExistsError                           Traceback (most recent call last)
<ipython-input-23-5aa728677edf> in <module>
      4 import os
      5 # Creating a directory
----> 6 os.mkdir('directory_name')
      7 # Changing the current directory
      8 os.chdir('path')

FileExistsError: [WinError 183] Cannot create a file when that file already exists: 'directory_name'

Example Using `sys` Module#

The sys module provides functions and variables used to manipulate different parts of the Python runtime environment.

sys.argv function returns a list of command line arguments passed to a Python script. The item at index 0 in this list is always the name of the script, at index 1 is the argument passed from the command line.

import sys
sys.path

['C:\\Users\\Deepak\\01_Learn_Python4Data\\04_Python_Functions',
 'C:\\ProgramData\\Anaconda3\\python38.zip',
 'C:\\ProgramData\\Anaconda3\\DLLs',
 'C:\\ProgramData\\Anaconda3\\lib',
 'C:\\ProgramData\\Anaconda3',
 '',
 'C:\\Users\\Deepak\\AppData\\Roaming\\Python\\Python38\\site-packages',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\locket-0.2.1-py3.8.egg',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32\\lib',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\Pythonwin',
 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\IPython\\extensions',
 'C:\\Users\\Deepak\\.ipython']

First, create a Python module with the name script.py and write the below code in that file.

>>> import sys
>>> # print(sys.argv[0], argv[1],sys.argv[2])  # this line would print out: filename argument1 argument2
>>> print('Welcome {}. Enjoy  {} for Data Science ^_^'.format(sys.argv[1], sys.argv[2]))

Second, open Anaconda Prompt (Anaconda3)

Third, type system path after cd

cd C:\\Users\\Deepak\\01_Learn_Python4Data\\04_Python_Functions

Forth, type

python script.py Milaan Python

Output:

Welcome Milaan. Enjoy  Python for Data Science ^_^

Some useful sys commands to type in:

# to exit sys
sys.exit()
# To know the largest integer variable it takes
sys.maxsize
# To know environment path
sys.path
# To know the version of python you are using
sys.version

Example Using `operator` Module#

# Example 1:

from operator import *
a, b = 10, 20
#prints the product of the values 'a' and 'b'
print(mul(a, b))
#prints True if the value of 'a' is greater than 'b'. Else, False
print(gt(a, b))
#prints the remainder value, when the value of 'a' is divided by 'b'
print(mod(a, b))
#concatenates and prints the given two strings
print(concat("Hello ", "World"))

200
False
10
Hello World

Example Using `string` Module#

A string module is a useful module for many purposes. The example below shows some use of the string module.

# Example 1:

from string import *
print(capwords("hello world")) #capitalizes the first letter of each words
print(ascii_letters) #prints all lowercase and uppercase letters

Hello World
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

# Example 2:

import string
print(string.ascii_letters) # abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
print(string.digits)        # 0123456789
print(string.punctuation)   # !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
0123456789
!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

Example Using `decimal` Module#

# Example 1:

from decimal import *
a, b = 10, 3
c = a / b
print(c)
print(Decimal(c)) #prints the complete decimal value of c

3.3333333333333335
3.333333333333333481363069950020872056484222412109375

Example Using `random` Module#

The random module is used to generate the random numbers. It provides the following two built in functions:

Comparision operators in Python#

Function	Description
`random()`	It returns a random number between 0.0 and 1.0 where 1.0 is exclusive.
`randint(x,y)`	It returns a random number between x and y where both the numbers are inclusive.

# Example 1:

from random import *
print(randint(10, 20)) #prints a random number between the given range

list1 = [30, 23, 45, 16, 89, 56]
print(choice(list1)) #prints a random element from the given iterator

print(uniform(10, 20)) #prints a random float number between two given values

10
16
13.03505598723366

# Example 2:

import random

print(random.random())
print(random.randint(2,8))

0.2946014910624595
8

# Example 3:

from random import randint   # import randint function

print(random())   # it doesn't take any arguments; it returns a value between 0 and 0.9999

# call randint function to get random number
print(randint(10, 30))  # it returns a random integer number between [10, 30] inclusive

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-31-92fab552c144> in <module>
      3 from random import randint   # import randint function
      4 
----> 5 print(random())   # it doesn't take any arguments; it returns a value between 0 and 0.9999
      6 
      7 # call randint function to get random number

TypeError: 'module' object is not callable

Example Using `math` Module#

Using math module, you can use different built in mathematical functions.

math module Functions:#

Function	Description
`ceil(n)`	It returns the next integer number of the given number.
`sqrt(n)`	It returns the Square root of the given number.
`exp(n)`	It returns the natural logarithm e raised to the given number.
`floor(n)`	It returns the previous integer number of the given number.
`log(n,baseto)`	It returns the previous integer number of the given number.
`pow(baseto, exp)`	It returns baseto raised to the exp power.
`sin(n)`	It returns sine of the given radian.
`cos(n)`	It returns cosine of the given radian.
`tan(n)`	It returns tangent of the given radian.

# Example 1:

from math import *
print(sqrt(16)) # prints the square root of the value 16 in the form of a floating-point value
print(factorial(5)) # prints the factorial of the value 5

4.0
120

# Example 2:

import math

a=4.6
print(math.ceil(a))       # 5, rounding to the highest
print(math.floor(a))      # 4, rounding to the lowest
b=9
print(math.sqrt(b))       # 3.0, square root
print(math.exp(3.0))      # 20.085536923187668
print(math.log(2.0))      # 0.6931471805599453
print(math.pow(2.0,3.0))  # 8.0, exponential function
print(math.sin(0))        # 0.0
print(math.cos(0))        # 1.0
print (math.tan(45))      # 1.6197751905438615
print(math.log10(100))    # 2.0, logarithm with 10 as base 

5
4
0
085536923187668
6931471805599453
0
0
0
6197751905438615
0

Constants -#

The math module provides two constants for mathematical Operations:

math.pi : Returns constant Pi = 3.14159…
math.e : Returns constant e= 2.71828…

# Example 3:

import math 

print("math.pi : ",math.pi)  # 3.141592653589793, pi constant
print("math.e : ",math.e)    # 2.718281828459045, e  constant

math.pi :  3.141592653589793
math.e :  2.718281828459045

Example Using `statistics` Module#

The statistics module provides functions for mathematical statistics of numeric data. The popular statistical functions which are defined in this module: mean, median, mode, stdev etc.

# Example 1:

from statistics import * # importing all the statistics modules
ages = [20, 20, 4, 24, 25, 22, 26, 20, 23, 22, 26]
print(mean(ages))       # ~22.9
print(median(ages))     # 23
print(mode(ages))       # 20
print(stdev(ages))      # ~2.3

21.09090909090909
22
20
6.106628291529549

Wrap up#

Since Python provides a lot of built-in modules, it is advisable to use built-in modules rather than user-created modules to perform basic operations.

Python Modules

Contents

Python Modules#

What are modules in Python?#

Advantage#

Creating a module in Python#

How to import modules in Python?#

Python import statement#

import multiple modules#

Python from-import statement#

import with renaming#

import all names#

Python Module Search Path#

Reloading a module#

The dir() built-in function#

Python Modules List#

Python Built-In Modules Examples#

Example Using os Module#

Example Using sys Module#

Example Using operator Module#

Example Using string Module#

Example Using decimal Module#

Example Using random Module#

Comparision operators in Python#

Example Using math Module#

math module Functions:#

Constants -#

Example Using statistics Module#

Wrap up#

Python `import` statement#

`import` multiple modules#

Python `from-import` statement#

`import` with renaming#

`import` all names#

The `dir()` built-in function#

Example Using `os` Module#

Example Using `sys` Module#

Example Using `operator` Module#

Example Using `string` Module#

Example Using `decimal` Module#

Example Using `random` Module#

Example Using `math` Module#

Example Using `statistics` Module#