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# numpy.memmap.strides

attribute

memmap.strides

  Tuple of bytes to step in each dimension when traversing an array.

  The byte offset of element `(i[0], i[1], ..., i[n])` in an array a is:

      offset = sum(np.array(i) * a.strides)

  A more detailed explanation of strides can be found in The N-dimensional array (ndarray).

  Warning

  Setting `arr.strides` is discouraged and may be deprecated in the future. `numpy.lib.stride_tricks.as_strided` should be preferred to create a new view of the same data in a safer way.

  See also

  `numpy.lib.stride_tricks.as_strided`

  Notes

  Imagine an array of 32-bit integers (each 4 bytes):

      x = np.array([[0, 1, 2, 3, 4],
                    [5, 6, 7, 8, 9]], dtype=np.int32)

  This array is stored in memory as 40 bytes, one after the other (known as a contiguous block of memory). The strides of an array tell us how many bytes we have to skip in memory to move to the next position along a certain axis. For example, we have to skip 4 bytes (1 value) to move to the next column, but 20 bytes (5 values) to get to the same position in the next row. As such, the strides for the array x will be `(20, 4)`.

  Examples

      >>> import numpy as np
      >>> y = np.reshape(np.arange(2 * 3 * 4, dtype=np.int32), (2, 3, 4))
      >>> y
      array([[[ 0,  1,  2,  3],
              [ 4,  5,  6,  7],
              [ 8,  9, 10, 11]],
             [[12, 13, 14, 15],
              [16, 17, 18, 19],
              [20, 21, 22, 23]]], dtype=np.int32)
      >>> y.strides
      (48, 16, 4)
      >>> y[1, 1, 1]
      np.int32(17)
      >>> offset = sum(y.strides * np.array((1, 1, 1)))
      >>> offset // y.itemsize
      np.int64(17)

      >>> x = np.reshape(np.arange(5*6*7*8, dtype=np.int32), (5, 6, 7, 8))
      >>> x = x.transpose(2, 3, 1, 0)
      >>> x.strides
      (32, 4, 224, 1344)
      >>> i = np.array([3, 5, 2, 2], dtype=np.int32)
      >>> offset = sum(i * x.strides)
      >>> x[3, 5, 2, 2]
      np.int32(813)
      >>> offset // x.itemsize
      np.int64(813)