Python Generators | Step by Step Guide of Generators in Python

Python Generators – Table of Content

Generators

The main purpose of a generator is to help us in creating our own iterators. It is a special type of function that returns an iterable set.The iterators that we create with the generator are referred to as lazy iterators. The contents of lazy iterators will not be stored in memory.If you want to iterate through large files, data streams, CSV files, etc., generators will be a good choice.Generators are introduced in PEP 255 and they are available since python 2.2 version.

How to create generator functions

Let us create a sample generator. Create a new file in any text editor and copy the below code.

def sample():a = ["Hello", "Welcome"]
yield a
for i in sample(): 
print("This is a sample generator")

In this code, the sample() is the generator function name. Yield is used to return items to the caller. Unlike return in normal function, you won’t exit the function here. Once a generator is defined, it is called similar to a normal function. But the execution gets paused when it encounters a yield keyword.

Save the file with script.py as the name. Open command prompt, navigate to the script file location path, and execute the below command.

python script.py

You should be able to see an output that says ‘This is a sample generator’ on the command prompt. Let us look at one more example that returns squared root numbers to the range of numbers defined.

def Squared_numbers(num):for num in range(num):
yield num**2
for i in Squared_numbers(5):
print(i)

This program calls Squared_numbers generator with 5 as a range. The generator will iterate from 0 and yields the square root of 5 numbers. The output for this program will be as follows.

Importance of yield statements in generators

Yield controls the flow of a generator function. When we call a generator expression or a generator function, we will get an iterator in return. This is nothing but a generator.

We have to assign the generator to a variable and then use it. When we call a generator function, it only gets executed until it encounters a yield statement. The yielded value is sent back to the caller.

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