Python ValueError: read length must be non-negative or -1 - File Reading Error

This error message occurs when attempting to read data from a file using the 'read()' method, but providing an invalid value for the read length. The 'read()' method takes an optional argument that specifies the number of bytes to read from the file.

The error message specifically indicates that the read length provided is either negative or equal to -1. This is not allowed since the read length must be a non-negative integer, or -1 to indicate reading the entire file.

To fix this error, ensure that the read length provided is a non-negative integer or -1. Here is an example of using the 'read()' method to read the entire contents of a file:

with open('file.txt', 'r') as f:
    contents = f.read(-1) # read entire file

In this example, the 'read()' method is called with the argument '-1' to read the entire file. If the read length is not explicitly specified, it defaults to -1.