How to combine regexps?

[MRAB]

kj wrote:
> In <h5cotl$or0$1 at reader1.panix.com> kj <no.email at please.post> writes:
> 
> 
> 
>> One of the nice things one can do with Perl's regexp's is illustrated
>> in the following example:
> 
>> my $gly = qr/gg[ucag]/i
>> my $ala = qr/gc[ucag]/i;
>> my $val = qr/gu[ucag]/i;
>> my $leu = qr/uu[ag]|cu[ucag]/i;
>> my $ile = qr/au[uca]/i;
> 
>> my $aliphatic = qr/$gly|$ala|$val|$leu|$ile/;
> 
> 
>> In other words, one can build regular expressions by re-combining
>> other regular expressions.
> 
>> Is there a way to do this with Python's regexps?
> 
> 
> OK, answering my own question here, it looks like the only way to
> do this is to leave the "component" expressions as regular strings,
> and combine those, before compiling them into regexps.
> 
> Easy enough.
> 
A compiled regular expression has 'pattern' and 'flags' attributes, so
you can get the original parameters which were used to create it if a
function is given just the compiled regular expression. Might be useful.