What are generators in Python

Question

I am new to Python. I just came across generators in Python. But I  am not able to understand it completely. Can anyone explain to me it in simple words?

Answer 1

There are two terms involved when we discuss generators.

1. Generator-Function : A generator-function is defined like a normal function, but whenever it needs to generate a value, it does so with the yield keyword rather than return. If the body of a def contains yield, the function automatically becomes a generator function.
2. Generator-Object : Generator functions return a generator object. Generator objects are used either by calling the next method on the generator object or using the generator object in a “for in” loop 

So a generator function returns a generator object that is iterable, i.e., can be used as an Iterator

# A simple generator for Fibonacci Numbers 
def fib(limit): 
      
    # Initialize first two Fibonacci Numbers  
    a, b = 0, 1
  
    # One by one yield next Fibonacci Number 
    while a < limit: 
        yield a 
        a, b = b, a + b 
  
# Create a generator object 
x = fib(5) 
  
# Iterating over the generator object using next 
print(x.next()); # In Python 3, __next__() 
print(x.next()); 
print(x.next()); 
print(x.next()); 
print(x.next()); 
  
# Iterating over the generator object using for 
# in loop. 
print("\nUsing for in loop") 
for i in fib(5):  
    print(i) 

Output :

0
1
1
2
3

Using for in loop
0
1
1
2
3