[Tutor] I am a friendly inoffensive non-commercial subject li ne

[alan.gauld@bt.com]

> The current high-level file commands force you to deal with a 
> class of  questions that the Python Elves usually keep 
> submerged: 

Yep, so maybe there's a reason...

> Of course it's good to have the choice of low-level, 
> byte-by-byte control, but that is what the os module is for. 


> Python was being invented, throwing a thin wrapper around 
> the C functions that  everybody involved knew was a good idea 

Actually altho' Python does wrap the C stuff the file 
methods are very similar to every mainstream programming 
language around from ADA to Lisp, to Smalltalk...

> We recognize two different types of flies: 
> 
> 1) "Normal" files which consist of lines, ...text
> 2) "Binary" files which consist of bytes. 


Pascal kind of makes that distinction by having text 
files as a special category. But binary files are 
broken into myriad types... FILE OF <FOO>

> Now when we want to access a file, we don't "open" it - 
> that's the Elves' job - we just get right down to it:
> 
> filehandle = file('/home/scot/python/wetcat.text')  or
> binhandle = binfile('flooddata.dat')
> 
> With this type of file, we can iterate, splice, or index the content 
> without having to explicitly tell the Elves that we want to 
> read or write or whatnot:

Thats actually quite tricky to do. Why not try implememting 
the interface in Python to see whats involved.... I had to 
build a "generic" file class in C++ once - it grew to 
well over 1000 lines!

One problem is that under the covers you have to figure out predictively
what mode to open the raw file in - what 
does the user want to do with it. Otherwise you have to 
open/close the file after each operation and keep track 
of where the last access was etc etc...

> >>>filehandle[2] 
> 'drip drip drip'
> >>>filehandle[0:2]
> ['drip', 'drip drip']

Not too hard if its text and you assume line by line 
access rather than characters, binary presumably 
returns bytes?

> Since we have direct (random) access with splices and 
> indices, we don't need to 'seek' and 'tell' anymore, 

Ah, but now try implementing that on a binary file.
But I guess you could just seek(0) after each 
operation... or could you? It might depend on the 
current mode...

> Reading is easy; writing gets you into trouble, 

Yes, especially with indexing type access.

BTW Have you looked at the fileinput module which 
does a little bit of what you want I think....

Alan g.