How To Import Modules in Python 3

How To Import Modules in Python 3

Introduction

The Python programming language comes with a variety of built-in functions. Among these are several common functions, including:

  • print() which prints expressions out
  • abs() which returns the absolute value of a number
  • int() which converts another data type to an integer
  • len() which returns the length of a sequence or collection

    • Prerequisites

    You should have Python 3 installed and a programming environment set up on your computer or server. If you don’t have a programming environment set up, you can refer to the installation and setup guides for a local programming environment or for a programming environment on your server appropriate for your operating system (Ubuntu, CentOS, Debian, etc.)

    Checking For and Installing Modules

    There are a number of modules that are built into the Python Standard Library, which contains many modules that provide access to system functionality or provide standardized solutions. The Python Standard Library is part of every Python installation.

    To check that these Python modules are ready to go, enter into your local Python 3 programming environment or server-based programming environment and start the Python interpreter in your command line like so:

    (my_env) sammy@Ubuntu:~/environments $ python

    From within the interpreter you can run the import statement to make sure that the given module is ready to be called, as in:

    >>> import math

    Let’s run the import statement with a module that you may not have installed, like the 2D plotting library matplotlib:

    >>> import matplotlib

    If matplotlib is not installed, you’ll receive an error like this:

    Output

    ImportError: No module named 'matplotlib'

    You can deactivate the Python interpreter with CTRL + D and then install matplotlib with pip. Next, we can use pip to install the matplotlib module:

    (my_env) sammy@Ubuntu:~/environments $ pip install matplotlib

    Once it is installed, you can import matplotlib in the Python interpreter using import matplotlib, and it will complete without error.

    Importing Modules

    To make use of the functions in a module, you’ll need to import the module with an import statement.

    An import statement is made up of the import keyword along with the name of the module.

    In a Python file, this will be declared at the top of the code, under any shebang lines or general comments

    So, in the Python program file my_rand_int.py we would import the random module to generate random numbers in this manner:

    import random

    In practice, with the example of the random module, this may look like a function such as:

  • random.randint() which calls the function to return a random integer, or
  • random.randrange() which calls the function to return a random element from a specified range

    • Let’s create a for loop to show how we will call a function of the random module within our my_rand_int.py program:

    for i in range(10):

    print(random.randint(1, 25))

    When we run the program with python my_rand_int.py, we’ll receive 10 random integers as output. Because these are random you’ll likely get different integers each time you run the program, but they’ll generate something like this:

    Output

    6,9,1,14,3,22,10,1,15,9

    If you would like to use functions from more than one module, you can do so by adding multiple import statements

    import random

    import math

    To make use of our additional module, we can add the constant pi from math to our program, and decrease the number of random integers printed out:

    import random

    import math

    for i in range(5):

    print(random.randint(1, 25))

    print(math.pi)

    Now, when we run our program, we’ll receive output that looks like this, with an approximation of pi as our last line of output:

    Output

    10,7,13,10,3.141592653589793

    The import statement allows you to import one or more modules into your Python program, letting you make use of the definitions constructed in those modules.

    Using from … import

    To refer to items from a module within your program’s namespace, you can use the from … import statement. When you import modules this way, you can refer to the functions by name rather than through dot notation

    In other programs, you may see the import statement take in references to everything defined within the module by using an asterisk (*) as a wildcard, but this is discouraged by PEP 8

    Let’s first review at importing one specific function, randint() from the random module:

    from random import randint

    Now, when we implement this function within our program, we will no longer write the function in dot notation as random.randint() but instead will only write randint():

    from random import randint

    for i in range(10):

    print(randint(1, 25))

    Using the from … import construction allows us to reference the defined elements of a module within our program’s namespace, letting us avoid dot notation.

    Aliasing Modules

    You may want to change a name because you have already used the same name for something else in your program, another module you have imported also uses that name, or you may want to abbreviate a longer name that you are using a lot.

    The construction of this statement looks like the following:

    import [module] as [another_name]

    Let’s modify the name of the math module in our my_math.py program file. We’ll change the module name of math to m in order to abbreviate it. Our modified program will look like this

    import math as m

    print(m.pi)

    print(m.e)

    Within the program, we now refer to the pi constant as m.pi rather than math.pi

    import matplotlib.pyplot as plt

    This allows programmers to append the shorter word plt to any of the functions available within the module, as in plt.show(). You can see this alias import statement in use within our “How to Plot Data in Python 3 Using matplotlib tutorial.”

    Conclusion

    When we import modules we’re able to call functions that are not built into Python. Some modules are installed as part of Python, and some we will install through pip

    Making use of modules allows us to make our programs more robust and powerful as we’re leveraging existing code. We can also create our own modules for ourselves and for other programmers to use in future programs