Numpy equivalent of list.index

Question

In a low-level function that is called many times, I need to do the equivalent of python\'s list.index, but with a numpy array. The function needs to return when it finds the f

Answer 1

You can code it in Cython and just import from a Python script. There is no need to migrate your entire project into Cython.

# paste into: indexing.pyx
def index(long[:] lst, long value):
    cdef int i
    for i in range(len(lst)):
        if lst[i] == value:
            return i
    raise ValueError

# import in your .py code
import pyximport
pyximport.install()
from indexing import index

# example
from numpy import zeros
a = zeros(10**6, int)
a[-1] = 1

index(a, 1)
Wall time: 6.07 ms
999999

index(a, 0)
Wall time: 38.1 µs
0