[Tutor] Using read() before closing a file

[Alan Gauld]

"Eduardo Vieira" <eduardo.susan at gmail.com> wrote 
>>>> arq = open('c:/myscripts/simple2.ttt', 'w')
>>>> arq.write('The length is %d' % len(a))
>>>> res = arq.read()
>>>> print res
> 
> The print doesn't print the text I had written, 

That's because of two things:
a) You opened the file for write only not reading
b) You had moved the file cursor beyond the text you wrote

On (b): the file is conceptually a sequential data stream 
so think of the cursor in a text editor line. After you have 
written something you cannot select what you have 
written unless you cursor back to the beginning. 
Similarly with a file. Even if you opened it with rw 
access you would still need to position the cursor
(with the seek() call) to the point before what you 
wrote to be able to read it. After reading it the cursor 
would once again be at the end of the file and you 
could write more data.

> But if I had closed the file and
> then did this: res = open('c:/myscripts/simple2.ttt').read(), it would
> have worked.

Thats right because you now open the file for reading, 
therefore the cursor is repositioned at he start of the file and 
the mode is set correctly.

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/