What is the primary function of 'a' mode when opening a file?

The 'a' mode, when opening a file in Python, is specifically designed for appending data. This means that when a file is opened in 'a' mode, any data written to the file is added to the end of the existing content, rather than replacing it. This is beneficial when you want to preserve the current data within the file and simply add more information to it, such as new entries in a log or additional records in a dataset.

Using 'a' mode ensures that the original content of the file remains intact and that your new data is seamlessly added. This makes it a straightforward option for situations where data needs to be accumulated over time without the risk of loss from previous entries or data truncation.