Map() in python gives output once only

Question

I was playing with map() function in Python 3.6.3 when I came across this below situation ::

>>> a = [12, 23, 13, 14, 15, 36]
>>> b = [34, 45, 35, 32, 34, 34]
>>> c = [34, 67, 89, 98, 98, 78]
>>> map(lambda x,y,z:x+y+z, a,b,c )
<map object at 0x0000017DD976EC88>
>>> e=map(lambda x,y,z:x+y+z, a,b,c )
>>> list(e)
[80, 135, 137, 144, 147, 148]
>>> list(e)
[]

My question is that why I cannot get output when I used list(e) second time. It’s showing empty list.

Can anyone help me with this?

Asked By: Dibakar Bose

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Source

Answer 1

Because In Python 3, map returns an iterator, which you can only iterate over once. If you iterate over an iterator a second time, it will raise StopIteration immediately, as though it were empty. Thats why you get empty list second time when you call it.
For more info see this question

I hope this helps you! 🙂

Answered By: Abdullah Ahmed Ghaznavi

Map() in python gives output once only

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