Can't understand why I can't assign map result to a variable. It's losing its value.
>>> L = 'something'
>>> R = map(lambda x: x * 2, L)
>>> print(list(R))
['ss', 'oo', 'mm', 'ee', 'tt', 'hh', 'ii', 'nn', 'gg']
>>> V = list(R)
>>> print(V)
[]
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4`map` creates an iterator, not a list; you can only consume it once. – jonrsharpe Apr 24 '19 at 08:57
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Calling `V = list(R)` the first time, then `print(V)`, would work fine. – smci Apr 24 '19 at 08:58
2 Answers
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Because the map object can be iterated over only once. When you print it, that's it. The next time you assign it, it's empty
Instead, try
R = map(..)
V = list(R)
print(V)
blue_note
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In Python 3 map returns an iterator that, once consumed, will yield nothing.
In your case you are consuming it in the first print(list(R)) call, so in the second one it yields nothing which is the same as list() alone.
jonrsharpe
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