What is the effect of using 'w' mode?

Using 'w' mode when opening a file has a specific behavior: it creates a new file or truncates an existing one. This means if the file does not already exist, it will be created. If the file does exist, its contents will be removed, and it will be ready for new content to be written.

This mode is essential when you want to ensure that you start from a clean state and write fresh data without retaining any previous information. It’s particularly useful in scenarios where old data is no longer relevant, allowing you to overwrite it seamlessly.

In contrast, other options focus on different file access modes. For instance, opening a file for reading does not allow modifications, while opening for writing without truncating (in 'a' mode) would append data without removing it. Accessing the file for reading and writing simultaneously (in 'r+' mode) also differs from 'w' mode since it does not truncate or create a file if it doesn't exist. Hence, the behavior of 'w' mode is clearly defined in creating or truncating files, which aligns with the selected answer.