Generators in Python

Generators in Python

Generators are functions that return a sequence of values . A generator function is written like an ordinary function but it uses 'yield' statement . This statement is useful to return a value .

Example , one can write a generator function to return numbers from x to y .

# here , the generator function name is  'mygen'

def mygen(x,y):

    while x <= y :

    yield x 

    x = x + 1        # increment value of x by 1

One can call this function by passing the values 5 and 10 as follows :

gen_obj = mygen(5,10)

Here , the mygen() function returns a generator object that contains sequence of numbers as returned by 'yield' statement . So 'gen_obj' refers to the generator object with a sequence of numbers from 5 to 10 . One can display the numbers from the "gen_obj" .One can display the numbers from "gen_obj" using display the numbers from "gen_obj" using a for loop as :

for i in g:

    print(i,end=' ')

In the following program , one can create a generator function that generates numbers from x to y and display those numbers .

Python program to create a generator that returns a sequence of numbers from x to y

# generator returns sequence from x to y

def mygen(x,y):

    while x <= y:

    yield x

    x = x + 1

# fill generator object with 5 and 10

gen_obj = mygen(5,10)

# display all numbers in the generator

for i in gen_obj:

    print(i,end = ' ')

Output

5 6 7 8 9 10

Once the generator object is created , we can store the elements of the generator into a list and use the list as we want . For example , to store the numbers of generator 'gen_obj' into a list 'lst' one can use the list() function as :

lst = list(gen_obj)

Now , the list 'lst' contains the elements:

[5 6 7 8 9 10]

If we want to retrieve element by element from a generator object , one can use the next() function as :

print(next(gen_obj))

which would display the first element in "gen_obj". And , when we call the above function the very next time , it will display the second element in "gen_obj" and by repeatedly calling the next() function , we would be able to display all the elements of "gen_obj" .

In the following program , a simple generator is created that returns 'A','B','C'

def mygen():

     yield 'A'

     yield 'B'

     yield 'C'

Here , mygen() is returning 'A','B','C' using yield statements . Here , yield statement returns the elements from a generator function into a generator object . And , when we call the mygen() function , it is expressed as follows :

gen_obj = mygen()

Here , the characters 'A','B','C' are present within the generator object "gen_obj" and they can be referred and called into use using the next(gen_obj) function to refer to the elements .