Add copies of a dimension in Python - numpy.ndarray

Question

I have an image (numpy.ndarray) shaped like this:

In : print(img.shape)
Out : (240, 320, 1)

In : print(img) # The output it's simplified
Out:[[[121]
      [119]
      [118]
      ..., 
      [ 39]
      [ 43]
      [ 44]]

And I need to add copies to look like this:

shape (240, 320, 3) 
    [[[121   121   121]
      [119   119   119]
      [118   118   118]
      ..., 
      [ 39   39   39]
      [ 43   43   43]
      [ 44   44   44]]

Any tips on how to achieve that?