When you use write() on an open file in 'w' mode, what happens to existing data within the file?

When a file is opened in 'w' (write) mode in Python, the behavior is designed to overwrite the contents of the file. Therefore, when the write() method is called on a file opened in this mode, it first clears any existing data within the file before writing the new data. This means that if the file had any content already, it will be entirely removed, and the new data will be written from the beginning of the file, effectively replacing whatever was there before. This feature is particularly useful when you want to start afresh with a file without maintaining the previous content.

In contrast, other modes such as 'a' (append) would add data to the end without modifying the current contents, which is not the case here. The 'r' (read) mode only supports reading from an existing file without altering it, reinforcing that 'w' mode is specifically intended for writing new data after clearing the old. Additionally, file locking is not a function of the write mode itself but rather a mechanism that must be implemented separately if needed.