len() compared with len on numpy array

Question

What is going on here? How can I check that a has length?

>>> import numpy as np
>>> a = np.array(3)
>>> hasattr(a , '__len__')
True
>>> len(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: len() of unsized object

Here, python considers a to not have length:

>>>a.shape
()

I am using python 2.7.3 and numpy 1.8.0.

Thanks.

Yair, both the title and this 2nd revision of your question deleted part of your question, so the answer appears unconnected to the question. Can you please fix it? It's very confusing. — smci
– smci, Commented Aug 25, 2018 at 2:29

user2489252 · Accepted Answer · 2014-10-20 22:33:37Z

1

Hm, maybe I am missing something here, but why don't you check for types?

import numpy as np

def make_ary(item):
    if not isinstance(item, list):
        ary = np.array([item])
    else:
        ary = np.array(item)
        ary = ary.ravel()
    return ary

And then:

a = [1,2,3]
b = 3
c = [ [1] , [2] ,[3] ]


>> make_ary(a)
array([1, 2, 3])

>> make_ary(b)
array([3])

>> make_ary(c)
array([1, 2, 3])

answered Oct 20, 2014 at 22:33

user2489252

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1 Comment

Yair Daon Over a year ago

Thanks for the answer but that was solved by a mysterious stranger that erased their comment. I'll just use np.ravel.

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