Python Module

Python Modules

A module is a file that contains Python code that we can use in our program. There are several built-in functions like print(), input(), and sum() that are readily available to us.

In addition to these functions, Python also has several functions that are defined inside a module which we can use after we import them.

Let's use one such module called math:

import math

number = 25
result = math.sqrt(number)
print(result)

print(math.pi)

Output

5.0
3.141592653589793

We imported the math module using the import statement. Once we import a module, we can use everything inside it using the dot operator.

result = math.sqrt(number)

As you can see from the code above, we used the code math.sqrt(number) to call the sqrt() function of the math module. This function calculates the square root of a number.

Also, the value of the constant pi is directly printed to the screen.

print(math.pi)

Renaming modules

While importing a module, we can also rename it to a different name as per our needs.

Let's rename the math module to m:

import math as m

number = 25

# use m.sqrt() instead of math.sqrt()
result = m.sqrt(number)

print(result)

# use m.pi instead of math.pi
print(m.pi)

Output

5.0
3.141592653589793

We get the same output as before.

Python from...import Statement

When we import a module like in our previous examples, everything in the module is available to us.

However, if we only need to import a specific definition like a function or a constant, we can use the from..import statement.

from math import sqrt

num = sqrt(64)
print(num)

Output

8.0

Here, only the sqrt() function is imported from the math module. When we use this syntax, we need to directly use the sqrt() function instead of math.sqrt().

We can also import multiple definitions from the module in a single line using this syntax:

from module_name import definition1, definition2, definition3, ...

Let's implement this in our program.

from math import pi, sin, sqrt

value = sin(pi/2)
print(value)

num = sqrt(64)
print(num)

Output

1.0
8.0

We can also use the from...import statement to import all definitions from a module using *:

from math import *

value = sin(pi/2)
print(value)

num = sqrt(64)
print(num)

Output

1.0
8.0

Here, the asterisk * means import everything.

Note: Importing every definition name with the asterisk symbol * is a bad programming practice and you should try to avoid it in your code.

The dir() function

The math module comes with many more handy functions and constants.

We can list out all the things defined inside a module by using the dir() function:

import math

print(dir(math))

Output

['__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']]

As you can see, there are many other mathematical, trigonometric and logarithmic functions inside the math module.

Custom Modules

In Python, we can also create our own custom modules as per our needs. This helps us to keep our code organized.

Let's make a module named calculator that will contain functions to perform arithmetic operations.

First, create a file named calculator.py in the same directory as your main Python file, and add the following:

def add(a, b):
    return a + b
    
def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b
    
def divide(a, b):
    return a / b

This file in itself is a module. Let's import this file from the main file. In my main file:

import calculator

result1 = calculator.add(2, 3)
print(result1)

result2 = calculator.subtract(6, 3)
print(result2)

result3 = calculator.multiply(10, 3)
print(result3)

result4 = calculator.divide(6, 3)
print(result4)

Output

5
3
30
2.0

In our example, we have only used functions and constants from a module. However a module may also contain classes or any other definitions.

Now, we can already sense how useful a module is. It helps us in better code management and improves the reusability of our code.

Recommended Reading: Python packages