[Tutor] Question on tell() function and error produced

[Jeff Shannon]

Henry Steigerwaldt wrote:

>To All:
>
>Can anyone tell me how to use the tell( ) function when 
>accessing data on the Web?
>
>I know how to use it when reading a file from the hard drive,
>but I get an error using it after reading text via the Web and
>then trying to use it on that particular "file object."
>

I believe that the file-like object that urllib provides does not 
support tell(), nor seek().  This is due to underlying limitations of 
using a data stream as a file -- there's no truly meaningful concept of 
"position" in a data stream.  Similarly, seek() and tell() don't -- 
can't -- work on sockets.

>I guess I could save the data to a file,
>then open the file and read it, THEN use the tell ( ) (and for that
>matter the seek( ) ) function like I am accustomed to doing
>successfully in the past. But I should be able to use it as is on the
>file object.
>

If you really need seek() and tell(), then you'll have to save the data 
to a disk file.  Remember, urllib and such don't provide an actual file 
object, just a "file-like" object.  This is one of the relatively few 
ways that it doesn't (can't) completely mimic a true file object.  (Of 
all file methods, seek() and tell() are the ones most often left 
unimplemented in file-like objects, most often because they hold no 
meaning to the form of the underlying data that the file-like object is 
wrapping.)

Jeff Shannon
Technician/Programmer
Credit International