Not clear on what documentation means here [pxlpluker]

[pxlpluker]

Not clear on what documentation means here.
What exactly does the underlined text mean. w & a obviously mean you are
going to update the file.
So what does the + mean on w+ & a+ mean?
Also please could someone explain w+ truncating the file.
I may just be dense so please be patient :)

-------------------------------------------------------------------------
[Copy from python 2.3.3 help file]
file( filename [, mode [, bufsize ] ] )

Return a new file object (described earlier under Built-in Types). The
first two arguments are the same as for stdio's fopen(): filename is the
file name to be opened, mode indicates how the file is to be opened: 'r'
for reading, 'w' for writing (truncating an existing file), and 'a'
opens it for appending (which on some Unix systems means that all writes
append to the end of the file, regardless of the current seek position).

Modes 'r+', 'w+' and 'a+' open the file for updating (note that 'w+'
truncates the file). Append 'b' to the mode to open the file in binary
mode, on systems that differentiate between binary and text files (else
it is ignored). If the file cannot be opened, IOError is raised.

[Daniel Dittmar]

pxlpluker wrote:

So what does the + mean on w+ & a+ mean? This means that you can write to the file, seek to a different position and
then read from the file without reopening.
Also please could someone explain w+ truncating the file.

This means that the file gets truncated.
If you open the file with w+ and write 10 bytes, the resulting file will
contain 10 bytes. If you open it with r+ and write 10 bytes, the resulting
file will contain the bytes you have just written and then bytes [10:] of
the original file.

Daniel