Yield Keyword in Python

Faisal Qureshi
faisal.qureshi@ontariotechu.ca
http://www.vclab.ca

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© Faisal Qureshi

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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Yield Keyword

• The yield keyword is used in the context of generator functions.
• A generator function is a special type of function that allows you to generate a series of values lazily, on-the-fly, as they are needed, instead of generating them all at once and storing them in memory.
• When a generator function is called, it returns an iterator object, which can be iterated over using a loop or by using functions like next().
• The yield keyword is what makes a function a generator function. When yield is used inside a function.
• The yield pauses the function's execution and returns a value to the caller. The next time the function is called, it picks up from where it left off, remembering its previous state.

Generate numbers method

def generate_numbers_1(a, b):
    result = []
    for i in range(a, b):
        result.append(i)
    return result

numbers = generate_numbers_1(30,35)
print(numbers)

[30, 31, 32, 33, 34]

for i in generate_numbers_1(30, 35):
    print(i,end=' ')

30 31 32 33 34 

for i in generate_numbers_1(10, 20):
    print(i, end=' ')

10 11 12 13 14 15 16 17 18 19 

Generate numbers method (using yield keyword)

def generate_numbers_2(a, b):
    for i in range(a, b):
        yield i

print(generate_numbers_2(30,35))

<generator object generate_numbers_2 at 0x107ca3e60>

for i in generate_numbers_2(10, 20):
    print(i, end=' ')

10 11 12 13 14 15 16 17 18 19