[Tutor] Regular expression to match \f in groff input?

[Bill Campbell]

I've been beating my head against the wall try to figure out how
to get regular expressions to match the font change sequences in
*roff input (e.g. \fB for bold, \fP to revert to previous font).
The re library maps r'\f' to the single form-feed character (as
it does other common single-character sequences like r'\n').

In perl, I can write something like this:

	s/\f[1NR]/</emphasis>/g;

This does not work in puthon:

	s = re.sub(r'\f[1NR]', '</emphasis>, sinput)

The string.replace() operator will handle the above replacement,
although it requires a separate replace for each of the possible
characters in the [1NR].

I have tried various options such as r'\\x66' and r'\\146', but
none of these work.

One work-around, assuming that the text does not contain control
characters, is to replace the \f characters with a control
character before doing the replacements, then replace that
control character with \f if any remain after processing:

import re, fileinput
for line in fileinput.input():
    line = line.rstrip()
    line = line.replace(r'\f', r'\001')
    # do something here to make substitutions
    line = line.replace(r'\001', r'\f')
    print line

Bill
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