numpy array float number division leads to strange behavior

Question

Please follow the code lines:

A = np.array([0 for i in range(10)])

A[:] = 0.1/2

A

Out[36]: array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0])

A[:] = float(0.2/2)

A[:]

Out[38]: array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0])

I can't understand, why numpy is giving such a strange behavior?

I am using numpy 1.13.3

Answer 1

Because when you define your array it is of dtype=int. Define it as float and it will work as you expect.

example:

a = np.arange(10) # dtype = int
a[:] = 0.1 # converts to int so to 0
print a

a = np.arange(10.) # dtype = float
# or equivalently a = np.arange(10, dtype=float)
a[:] = 0.1 # works as you expect
print a