what is update in filemode in python code example

Example: python file open modes

r for reading
r+ opens for reading and writing (cannot truncate a file)
w for writing
w+ for writing and reading (can truncate a file)
rb for reading a binary file. The file pointer is placed at the beginning of the file.
rb+ reading or writing a binary file
wb+ writing a binary file
a+ opens for appending
ab+ Opens a file for both appending and reading in binary. The file pointer is at the end of the file if the file exists. The file opens in the append mode.
x open for exclusive creation, failing if the file already exists (Python 3)