Python Equivalent for dd & fold

[seldan24]

On Jul 15, 1:48 pm, Emile van Sebille <em... at fenx.com> wrote:
> On 7/15/2009 10:23 AM MRAB said...
>
> >> On Jul 15, 12:47 pm, Michiel Overtoom <mot... at xs4all.nl> wrote:
> >>> seldan24 wrote:
> >>>> what can I use as the equivalent for the Unix 'fold' command?
> >>> def fold(s,len):
> >>>      while s:
> >>>          print s[:len]
> >>>          s=s[len:]
>
> <snip>
> > You might still need to tweak the above code as regards how line endings
> > are handled.
>
> You might also want to tweak it if the strings are _really_ long to
> simply slice out the substrings as opposed to reassigning the balance to
> a newly created s on each iteration.
>
> Emile

Thanks for all of the help.  I'm almost there.  I have it working now,
but the 'fold' piece is very slow.  When I use the 'fold' command in
shell it is almost instantaneous.  I was able to do the EBCDIC->ASCII
conversion usng the decode method in the built-in str type.  I didn't
have to import the codecs module.  I just decoded the data to cp037
which works fine.

So now, I'm left with a large file, consisting of one extremely long
line of ASCII data that needs to be sliced up into 35 character
lines.  I did the following, which works but takes a very long time:

f = open(ascii_file, 'w')
while ascii_data:
    f.write(ascii_data[:len])
    ascii_data = ascii_data[len:]
f.close()

I know that Emile suggested that I can slice out the substrings rather
than do the gradual trimming of the string variable as is being done
by moving around the length.  So, I'm going to give that a try... I'm
a bit confused by what that means, am guessing that slice can break up
a string based on characters; will research.  Thanks for the help thus
far.  I'll post again when all is working fine.