numpy.where() in Python

returns the indices of elements in an input array where the given condition is satisfied.

# Python program explaining 
# where() function 

import numpy as np 

np.where([[True, False], [True, True]], 
    [[1, 2], [3, 4]], [[5, 6], [7, 8]]) 

# Python program explaining 
# where() function 

import numpy as np 

# a is an array of integers. 
a = np.array([[1, 2, 3], [4, 5, 6]]) 

print(a) 

print ('Indices of elements <4') 

b = np.where(a<4) 
print(b) 

print("Elements which are <4") 
print(a[b]) 

References
https://www.geeksforgeeks.org/numpy-where-in-python/