CODEWITHSUNDEEP
pythongenerator
MichaelSB
MichaelSB

Reputation: 3181

Generator usage in Python

I'm learning about generators, so I defined the following function which calculates Fibonacci sequence:

def fib(max):
    a, b = 0, 1
    while a < max:
        yield a
        a, b = b, a + b

I tried to use it like this, but it didn't work:

next(fib(10))
Out[413]: 0

next(fib(10))
Out[414]: 0

next(fib(10))
Out[415]: 0

However, using it like this works as expected:

f = fib(10)

next(f)
Out[417]: 0

next(f)
Out[418]: 1

next(f)
Out[419]: 1

next(f)
Out[420]: 2

Why the first case does not work?

Upvotes: 1

Views: 65

Answers (2)

Michal Frystacky
Michal Frystacky

Reputation: 1467

next(iterator[, default])

Retrieve the next item from the iterator by calling its next() method. If default is given, it is returned if the iterator is exhausted, otherwise StopIteration is raised.

The first one works:

It just generates a new iterator for each of the functions instances you make when you callfib(10)

So, every time you call fib(10) you create a new fib function instance that returns an iterator specific to that instance.

Notice that they all return the first value correctly.

Upvotes: 2

Seekheart
Seekheart

Reputation: 1173

when you run it in the first case it starts again from the beginning and so it'll always just go start --> first, while in the second case everytime you call f, f is changing so it goes start --> first --> second --> third.

Upvotes: 0

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