Convert map object to numpy array in python 3

Question

In Python 2 I could do the following:

import numpy as np    
f = lambda x: x**2
seq = map(f, xrange(5))
seq = np.array(seq)
print seq
# prints: [ 0  1  4  9 16]

In Python 3 it does not work anymore:

import numpy as np    
f = lambda x: x**2
seq = map(f, range(5))
seq = np.array(seq)
print(seq)
# prints: <map object at 0x10341e310>

How do I get the old behaviour (converting the map results to numpy array)?

Edit: As @jonrsharpe pointed out in his answer this could be fixed if I converted seq to a list first:

seq = np.array(list(seq))

but I would prefer to avoid the extra call to list.

question from:https://stackoverflow.com/questions/28524378/convert-map-object-to-numpy-array-in-python-3

Answer 1

One more alternative, other than the valid solutions @jonrsharpe already pointed out is to use np.fromiter:

>>> import numpy as np    
>>> f = lambda x: x**2
>>> seq = map(f, range(5))
>>> np.fromiter(seq, dtype=np.int)
array([ 0,  1,  4,  9, 16])