What is the purpose of the open function when used with 'r' mode?

The purpose of the open function when used with 'r' mode is to read data from an existing file. When 'r' is specified as the mode, it indicates that the file is being opened for reading, and the function will try to open the file in a way that allows you to access its contents. If the file does not exist when attempting to open it in this mode, a FileNotFoundError will be raised, which highlights that 'r' mode strictly requires the file to be present for successful operation. This is contrasted with other modes like 'w' (write) or 'a' (append) which can create new files or modify existing ones.