Python Generators

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Generators are function used to create iterators, so that it can be used in the for loop.

Creating Generators

Generators are defined similar to function but there is only one difference, we use yield  keyword to return value used for each iteration of the for loop. Let’s see an example where we are trying to clone python’s built-in range()  function.

 

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def my_range(start, stop, step = 1):

    if stop <= start:

        raise RuntimeError("start must be smaller than stop")

    i = start

    while i < stop:

        yield i

        i += step

 

try:

    for k in my_range(10, 50, 3):

        print(k)

except RuntimeError as ex:

    print(ex)

except:

    print("Unknown error occurred")

Expected Output:

 

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Here is how my_range()  works:

In for loop my_range()  function get called, it initializes values of the three arguments(start , stop  and step ) and also checks whether stop  is smaller than or equal tostart , if it is not then i  is assigned value of start . At this point i  is 10 so while condition evaluates to True  and while loop starts executing. In next statementyield transfer control to the for loop and assigns current value of i to variable k , inside the for loop print statement get executed, then the control again passes to line 7 inside the function my_range()  where i  gets incremented. This process keeps on repeating until i <stop .