Python Generator Performance, Yield, One Line Generator

2022-10-26 365 words 2 minutes

Contents

Generator Performance

Generators are a great way to optimize memory. An infinite sequence generator is an extreme example of this optimization.

Yield

The yield statement suspends a function’s execution and sends a value back to the caller, but retains enough state to enable the function to resume where it left off.

When the function resumes, it continues execution immediately after the last yield run.

This allows its code to produce a series of values over time, rather than computing them at once and sending them back like a list in which we optimized memory usage.

One Line Generator

Iterate through a list and brace them in a (). (x for x in [1,2,3,4])

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print('one line generator')
olg = (x for x in [1,2,3,4])
print(f'type(olg) = {type(olg)}')
print(f'olg = {olg}')

for x in olg:
    print(x)

Output:

one line generator
type(olg) = <class ‘generator’>
olg = <generator object at 0x0000029BBC2C4B30>
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4

Same as

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olg = (x for x in [1,2,3,4])
print(next(olg))
print(next(olg))
print(next(olg))
print(next(olg))

Output:

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Function

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# A Simple Python program to demonstrate working
# of yield

# A generator function that yields 1 for the first time,
# 2 second time and 3 third time


def simpleGeneratorFun():
	yield 1
	yield 2
	yield 3


# Driver code to check above generator function
for value in simpleGeneratorFun():
	print(value)

Output:

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3

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def my_generator(n=0):
    while True:
        yield n
        n+1

for i, n in enumerate(my_generator(5)):
    print(n)
    if i == 10:
        break

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Appendix

Generator of Generators

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def metagen():
    def innergen():
        yield 1
        yield 2
        yield 3

    for i in range(3):
        r = innergen()
        yield r

        for _ in r: pass

https://stackoverflow.com/questions/19033401/python-generator-of-generators

Length of Generator

The easiest way is probably just sum(1 for _ in gen) where gen is your generator. https://stackoverflow.com/questions/393053/length-of-generator-output

Stepping Cycle Generator

Data-Structures-and-Algorithms-in-Python/Stepping Cycle Generator.py at main · chienhsiang-hung/Data-Structures-and-Algorithms-in-Python (github.com)