How to combine regexps?

[kj]

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?

TIA!

kynn