numpy.expand_dims

 numpy.expand_dims(a, axis)[source]

    Expand the shape of an array.

    Insert a new axis that will appear at the axis position in the expanded array shape.

    Note

    Previous to NumPy 1.13.0, neither axis < -a.ndim - 1 nor axis > a.ndim raised errors or put the new axis where documented. Those axis values are now deprecated and will raise an AxisError in the future.
    Parameters: 

    a : array_like

        Input array.

    axis : int

        Position in the expanded axes where the new axis is placed.

    Returns:    

    res : ndarray

        Output array. The number of dimensions is one greater than that of the input array.

Examples:

>>> x = np.array([1,2])
>>> x.shape
(2,)

>>> y = np.expand_dims(x, axis=0)
>>> y
array([[1, 2]])
>>> y.shape
(1, 2)

>>> y = np.expand_dims(x, axis=1)  # Equivalent to x[:,newaxis]
>>> y
array([[1],
       [2]])
>>> y.shape
(2, 1)