If an eval-able re.Regex is used, the flags can be showed as second arg, like:
  re.Regex('a', re.I|re.S)
instead of being added to the pattern as in
  re.Regex('(?is)a')

The repr can be generated with something like
  're.Regex({r.pattern!r}, {r.flags})'.format(r=r)
that currently prints
  re.Regex('abc', 50)
but if #11957 is fixed, the result will look like
  re.Regex('abc', re.I|re.S)
for a regex created with
  r = re.compile('abc', re.I|re.S)