Method __new__

numpy/core/memmap.py:209–287

(subtype, filename, dtype=uint8, mode='r+', offset=0,
                shape=None, order='C')

    __array_priority__ = -100.0

    def __new__(subtype, filename, dtype=uint8, mode='r+', offset=0,
                shape=None, order='C'):
        # Import here to minimize 'import numpy' overhead
        import mmap
        import os.path
        try:
            mode = mode_equivalents[mode]
        except KeyError as e:
            if mode not in valid_filemodes:
                raise ValueError(
                    "mode must be one of {!r} (got {!r})"
                    .format(valid_filemodes + list(mode_equivalents.keys()), mode)
                ) from None

        if mode == 'w+' and shape is None:
            raise ValueError("shape must be given if mode == 'w+'")

        if hasattr(filename, 'read'):
            f_ctx = nullcontext(filename)
        else:
            f_ctx = open(os_fspath(filename), ('r' if mode == 'c' else mode)+'b')

        with f_ctx as fid:
            fid.seek(0, 2)
            flen = fid.tell()
            descr = dtypedescr(dtype)
            _dbytes = descr.itemsize

            if shape is None:
                bytes = flen - offset
                if bytes % _dbytes:
                    raise ValueError("Size of available data is not a "
                            "multiple of the data-type size.")
                size = bytes // _dbytes
                shape = (size,)
            else:
                if not isinstance(shape, tuple):
                    shape = (shape,)
                size = np.intp(1)  # avoid default choice of np.int_, which might overflow
                for k in shape:
                    size *= k

            bytes = int(offset + size*_dbytes)

            if mode in ('w+', 'r+') and flen < bytes:
                fid.seek(bytes - 1, 0)
                fid.write(b'\0')
                fid.flush()

            if mode == 'c':
                acc = mmap.ACCESS_COPY
            elif mode == 'r':
                acc = mmap.ACCESS_READ
            else:
                acc = mmap.ACCESS_WRITE

            start = offset - offset % mmap.ALLOCATIONGRANULARITY
            bytes -= start