python open built-in function: difference between modes a, a+, w, w+, and r+?

Question

In the python built-in open function, what is the exact difference between the modes w, a, w+, a+, and r+?

In particular, the documentation implies that all of these will allow writing to the file, and says that it opens the files for "appending", "writing", and "updating" specifically, but does not define what these terms mean.

Answer 1

w: Opens in write-only mode. The pointer is placed at the beginning of the file and this will overwrite any existing file with the same name. It will create a new file if one with the same name doesn't exist.

a: Opens a file for appending new information to it. The pointer is placed at the end of the file. A new file is created if one with the same name doesn't exist.

w+: Opens a file for writing and reading.

a+: Opens a file for both appending and reading.

r+: Opens a file for reading and writing, placing the pointer at the beginning of the file.