Which mode is used in the open() function to write data to a file in Python?

The mode that is used in the open() function to write data to a file in Python is 'w'. Here is how you can use it:

1. First, you need to specify the name of the file that you want to write to. You can do this by passing the file name as a string to the open() function. For example, if you want to write to a file named 'example.txt', you would do this:

file = open('example.txt', 'w')

2. The 'w' in the open() function stands for 'write'. This means that the file is opened for writing. If the file already exists, the 'w' mode will overwrite the existing file. If the file does not exist, Python will create it.

3. After opening the file, you can write data to it using the write() method. For example, if you want to write the string 'Hello, world!' to the file, you would do this:

file.write('Hello, world!')

4. After you are done writing to the file, you should close it using the close() method. This is important because it frees up system resources that were used during the writing process. Here is how you can close the file:

file.close()

So, to summarize, the 'w' mode is used in the open() function to write data to a file in Python.