ndarraytofile

ndarray.tofile, commonly referred to as ndarraytofile, is a method of NumPy's ndarray class that writes the elements of an array to a file. It accepts a file name or a file-like object as its first argument. The second argument, sep, controls the output format: if sep is an empty string (the default), the array is written as raw binary data; if sep is non-empty, the array is written as text with values separated by sep using the specified format string (the default format is a representation suitable for Python).

The data are written in the array’s memory order. For typical C-contiguous arrays, this corresponds to row-major order when the array is flattened for writing. Binary mode writes a compact binary representation of the elements, without any metadata about shape or dtype. Text mode writes human-readable values but still does not embed shape information in the file.

Reading data written with tofile is done with numpy.fromfile, which requires the correct dtype. If the file was written in binary mode, specify the same dtype and reshape as needed. If the file was written in text mode, provide an appropriate sep to fromfile so the text can be parsed back into numbers.

Example:

import numpy as np

a = np.arange(6).reshape(2, 3)

a.tofile('out.bin')

b = np.fromfile('out.bin', dtype=a.dtype).reshape(a.shape)

a.tofile('out.txt', sep=',')

b_text = np.fromfile('out.txt', sep=',', dtype=a.dtype).reshape(a.shape)

Limitations include the lack of stored shape or dtype in the file, so reading requires prior knowledge of these attributes. For portable storage with metadata, NumPy offers alternatives such as numpy.save and numpy.load, or numpy.savetxt for text formats.