numpy.where() is my favorite.

```
>>> x = numpy.array([1,0,2,0,3,0,4,5,6,7,8])
>>> numpy.where(x == 0)[0]
array([1, 3, 5])
```

There is `np.argwhere`

,

```
import numpy as np
arr = np.array([[1,2,3], [0, 1, 0], [7, 0, 2]])
np.argwhere(arr == 0)
```

which returns all found indices as rows:

```
array([[1, 0], # Indices of the first zero
[1, 2], # Indices of the second zero
[2, 1]], # Indices of the third zero
dtype=int64)
```

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