[Tutor] File access codes in Python
alan.gauld@bt.com
alan.gauld@bt.com
Sun, 19 May 2002 18:19:38 +0100
> In Tcl, one can open a file for reading, writing,
> and both reading AND writing.
> However, in Python, it appears from the book I have, and
> from some online information, that one does not have the
> option to open a file for BOTH reading and writing.
You do, but its unusual and risky.
> it complicates the situation.
Actually having a file do both is the com,plicated bit,
even in Tcl. Its very easy to wind up overwriting a bit
of data you didn't mean to and you have to constantly
track your location in the file. Very messy and to be
avoided if posdsible IMHO.
> a program TWICE, just to read the file at one point,
> and then write to the same file at some other point
Its how most programs work(eg MS Word, Excel etc)
Its much safer since you work on a backup copy of the
data and can revert in the case of an error.
But if you must do it, check out the "r+" option of open()
Alan g.
Author of the 'Learning to Program' web site
http://www.freenetpages.co.uk/hp/alan.gauld