What does [:, :] mean on NumPy arrays

Question

Sorry for the stupid question. I\'m programming on PHP but found some nice code on Python and want to \"recreate\" it on PHP. But I\'m quite frustrated about the line

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Answer 1

The [:, :] stands for everything from the beginning to the end just like for lists. The difference is that the first : stands for first and the second : for the second dimension.

a = numpy.zeros((3, 3))

In [132]: a
Out[132]: 
array([[ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])

Assigning to second row:

In [133]: a[1, :] = 3

In [134]: a
Out[134]: 
array([[ 0.,  0.,  0.],
       [ 3.,  3.,  3.],
       [ 0.,  0.,  0.]])

Assigning to second column:

In [135]: a[:, 1] = 4

In [136]: a
Out[136]: 
array([[ 0.,  4.,  0.],
       [ 3.,  4.,  3.],
       [ 0.,  4.,  0.]])

Assigning to all:

In [137]: a[:] = 10

In [138]: a
Out[138]: 
array([[ 10.,  10.,  10.],
       [ 10.,  10.,  10.],
       [ 10.,  10.,  10.]])