What does 'r' mode do when opening a text file?

When opening a text file in 'r' mode, the primary function is to allow the program to read the content of the file. This means that you can access and retrieve the data stored within the file. The 'r' mode does not alter the file in any way; it only provides the ability to view its contents.

When a file is opened in 'r' mode, if the file does not exist, an error will be raised, signaling that the file cannot be found. However, if the file is there, you can read its contents line by line or as a whole, depending on the methods used.

This mode is vital in scenarios where the program only needs to read data without making any modifications or additions to the existing content, ensuring that the original data remains unchanged.