Python Tutorials

Yield in Python Tutorial

Generator & Yield vs Return Example

While working with a large amount of data the programmer sometimes needs to control the function’s start and stop state. The Yield gives the programmer the power to execute the program the way he/she wants rather than computing them at once. Let’s take a look at an example. Suppose you have a function that prints “Hello World” 5 times and functions that Yields “Hello World” five times. Let’s take a look at the difference between Yield and simple return for Yield in Python.

def normal():
print("Hello World")
print("Hello World")
print("Hello World")
print("Hello World")
print("Hello World")
def yielding():
yield "Hello World"
yield "Hello World"
yield "Hello World"
yield "Hello World"
yield "Hello World"

normal()
print("Now Calling Yeilding function")
print(yielding())
Yield in Python

Take a look at the above output. The normal function gives us back 5 print statements but the yielding function gives a generator.

Now we need to loop over the generator to get the output.

def yielding():
yield "Hello World"
yield "Hello World"
yield "Hello World"
yield "Hello World"
yield "Hello World"

print("Now Calling Yeilding function")
output = yielding()
for i in output:
print(i)
yield Hello World

How to read the values from the generator?

Let’s take a look at different ways to read values from generators.

Using : list()

We can use the list function to generate all the output and store it in a list.

def even_num(x):
for i in range(x):
  if (i%3==0):
      yield i
num = even_num(20)
print(num)
print(list(num))

Using : for-loop

In Yield in Python, We used for loop to iterate over the generator in the first example. Let’s take another example.

def even_num(x):
for i in range(x):
  if (i%3==0):
      yield i
num = even_num(20)
print(num)
for i in num:
print(i)
yield Hello World

Using next()

There is a built-in function next which is used to generate the next number from generator. After generating the last item it will give an error. 

def even_num(x):
for i in range(x):
  if (i%3==0):
      yield i
num = even_num(10)
print(num)
print(next(num))
print(next(num))
print(next(num))
print(next(num))
print(next(num))
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