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pythoniteratorgeneratorenumerate

Is enumerate in python lazy?

I'd like to know what happens when I pass the result of a generator function to python's enumerate(). Example:

def veryBigHello():
    i = 0
    while i < 10000000:
        i += 1
        yield "hello"

numbered = enumerate(veryBigHello())
for i, word in numbered:
    print i, word

Is the enumeration iterated lazily, or does it slurp everything into the <enumerate object> first? I'm 99.999% sure it's lazy, so can I treat it exactly the same as the generator function, or do I need to watch out for anything?

Solution

  • It's lazy. It's fairly easy to prove that's the case:

    >>> def abc():
...     letters = ['a','b','c']
...     for letter in letters:
...         print letter
...         yield letter
...
>>> numbered = enumerate(abc())
>>> for i, word in numbered:
...     print i, word
...
a
0 a
b
1 b
c
2 c