Class memmap

numpy/_core/memmap.py:24–362

Create a memory-map to an array stored in a *binary* file on disk. Memory-mapped files are used for accessing small segments of large files on disk, without reading the entire file into memory. NumPy's memmap's are array-like objects. This differs from Python's ``mmap`` module, wh

@set_module('numpy')
class memmap(ndarray):
    """Create a memory-map to an array stored in a *binary* file on disk.

    Memory-mapped files are used for accessing small segments of large files
    on disk, without reading the entire file into memory.  NumPy's
    memmap's are array-like objects.  This differs from Python's ``mmap``
    module, which uses file-like objects.

    This subclass of ndarray has some unpleasant interactions with
    some operations, because it doesn't quite fit properly as a subclass.
    An alternative to using this subclass is to create the ``mmap``
    object yourself, then create an ndarray with ndarray.__new__ directly,
    passing the object created in its 'buffer=' parameter.

    This class may at some point be turned into a factory function
    which returns a view into an mmap buffer.

    Flush the memmap instance to write the changes to the file. Currently there
    is no API to close the underlying ``mmap``. It is tricky to ensure the
    resource is actually closed, since it may be shared between different
    memmap instances.


    Parameters
    ----------
    filename : str, file-like object, or pathlib.Path instance
        The file name or file object to be used as the array data buffer.
    dtype : data-type, optional
        The data-type used to interpret the file contents.
        Default is `uint8`.
    mode : {'r+', 'r', 'w+', 'c'}, optional
        The file is opened in this mode:

        +------+-------------------------------------------------------------+
        | 'r'  | Open existing file for reading only.                        |
        +------+-------------------------------------------------------------+
        | 'r+' | Open existing file for reading and writing.                 |
        +------+-------------------------------------------------------------+
        | 'w+' | Create or overwrite existing file for reading and writing.  |
        |      | If ``mode == 'w+'`` then `shape` must also be specified.    |
        +------+-------------------------------------------------------------+
        | 'c'  | Copy-on-write: assignments affect data in memory, but       |
        |      | changes are not saved to disk.  The file on disk is         |
        |      | read-only.                                                  |
        +------+-------------------------------------------------------------+

        Default is 'r+'.
    offset : int, optional
        In the file, array data starts at this offset. Since `offset` is
        measured in bytes, it should normally be a multiple of the byte-size
        of `dtype`. When ``mode != 'r'``, even positive offsets beyond end of
        file are valid; The file will be extended to accommodate the
        additional data. By default, ``memmap`` will start at the beginning of
        the file, even if ``filename`` is a file pointer ``fp`` and
        ``fp.tell() != 0``.
    shape : int or sequence of ints, optional
        The desired shape of the array. If ``mode == 'r'`` and the number
        of remaining bytes after `offset` is not a multiple of the byte-size