Better regex with f-strings and re.VERBOSE

Combine f"{whatever}" with r"""...""" to make something like this:

code = r"""
[A-Z]*H  # prefix
\d+      # digits
[a-z]*   # suffix
"""

multicode = fr"""
(?: \( \s* )?               # maybe open paren and maybe space
{code}                      # one code
(?: \s* \+ \s* {code} )*    # maybe followed by other codes, plus-separated
(?: \s* [\):+] )?           # maybe space and maybe close paren or colon or plus
"""

pattern = fr"""
( {multicode} )             # code (capture)
( .*? )                     # message (capture): everything ...
(?=                         # ... up to (but excluding) ...
    {multicode}             # ... the next code
        (?! [^\w\s] )       # (but not when followed by punctuation)
    | $                     # ... or the end
)
"""

Caveats:

• have to escape hash and space. “When a line contains a # that is not in a character class and is not preceded by an unescaped backslash, all characters from the leftmost such # through the end of the line are ignored.”
• When composing regexes, ending a pattern on the same line as a comment might accidentally comment the following line in the enclosing pattern
• braces have to be doubled to escape them, because f-strings
• you can use inline flags: """(?x)..."""