To read a file’s contents, call f.read(size), which reads some quantity of data and returns it as a string (in text mode) or bytes object (in binary mode). size is an optional numeric argument. When size is omitted or negative, the entire contents of the file will be read and returned [...]. Otherwise, at most size bytes are read and returned.

Otherwise, at most size characters (in text mode) or size bytes (in binary mode) are read and returned.