numpy数组等效于+ =运算符

Question

I often do the following:

import numpy as np

def my_generator_fun():
    yield x # some magically generated x

A = []
for x in my_generator_fun():
    A += [x]
A = np.array(A)

Is there a better solution to this which operates on a numpy array from the start and avoids the creation of a standard python list?

Note that the += operator allows to extend an empty and dimensionless array with an arbitrarily dimensioned array whereas np.append and np.concatenate demand for equally dimensioned arrays.

Answer 1

Use np.fromiter :

def f(n):
    for j in range(n):
        yield j

>>> np.fromiter(f(5), dtype=np.intp)
array([0, 1, 2, 3, 4])

If you know beforehand the number of items the iterator is going to return, you can speed things up using the count keyword argument:

>>> np.fromiter(f(5), dtype=np.intp, count=5)
array([0, 1, 2, 3, 4])

Answer 2

To get the same array A , do:

A = numpy.arange(5)

Arrays are not in general meant to be dynamically sized, but you could use numpy.concatenate .