On Sat, 10 Oct 2026 00:25:54 -0000 (UTC), I wrote:

For comparison, here is an example of Python?s match-statement. Like
all the good (i.e. non-C-based) designs, the designers saw no point in
having fall-through.

This is a very simple example, involving straight matching of values
against instances of an enum. There are also more complex
pattern-matching options available.

Here?s an example that matches the type of the match-expression (not
its value) against various event subclasses:

events = iter(self.ws.events())
while True :
event = next(events, None)
if event == None :
break
match event :
case wsevents.AcceptConnection() :
self.logger.debug("connection accepted")
#end case

case wsevents.RejectConnection() :
raise RuntimeError \
(
"WebSockets connection rejected: code %d" % event.status_code
)
#end case

case wsevents.CloseConnection() :
self.logger.debug("connection closing")
if not self.closing :
self.closing = True
if ASYNC :
await self.sock.sendall(self.sock, self.ws.send(event.response()))
else :
self.sock.sendall(self.sock, self.ws.send(event.response()))
#end if
#end if
#end case

case wsevents.Ping() :
if ASYNC :
await self.sock.sendall(self.ws.send(event.response()))
else :
self.sock.sendall(self.ws.send(event.response()))
#end if
#end case

case wsevents.TextMessage() :
self.partial += event.data
if not event.message_finished :
break
if self.partial != "" :
result = json.loads(self.partial)
self.partial = ""
else :
result = None
#end if
yield result
#end case

case _ :
raise RuntimeError \
(
"unexpected WebSocket event %s -- %s"
%
(type(event).__name__, repr(event))
)
#end case
#end match
#end while

It is permissible to mix all the different kinds of matches in
different case-clauses within the same match-statement.

I?m still getting used to the match-statement, and I?m currently
thinking of dropping the ?#end case? line, since each case-clause is
implicitly terminated by the following one (or the end of the
match-statement) anyway. The ?#end match? will stay, of course.


--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 2026-10-11, Lawrence D?Oliveiro <ldo@nz.invalid> wrote:

Here?s an example that matches the type of the match-expression (not
its value) against various event subclasses:

events = iter(self.ws.events())
while True :
event = next(events, None)
if event == None :
break

Um.

Why would you do that and not:

for event in self.ws.events():

?

--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sat, 10 Oct 2026 00:25:54 -0000 (UTC), I wrote:

For comparison, here is an example of Python?s match-statement. Like
all the good (i.e. non-C-based) designs, the designers saw no point
in having fall-through.

This is a very simple example, involving straight matching of values
against instances of an enum. There are also more complex
pattern-matching options available.

Another, slightly more involved example, where the matching is against
the components of a tuple. This is from a parser for the Varlink
interface definition language. Note the use of the ?_? wildcard to
indicate don?t-care parts of matches:

match token.value, token.rule_name :
case "[]", _ :
nexttoken()
valtype = parse_typedef(None)
result = ArrayType(name, valtype)
case "[string]", _ :
nexttoken()
valtype = parse_typedef(None)
result = DictType(name, valtype)
case _, "elttypedef" :
result = parse_elttypedef(name)
case _, "typedef" :
result = parse_typedef(name)
case _ :
raise AssertionError \
(
"unrecognized typedef token %s: %s"
%
(token.rule_name, repr(token.value))
)
#end match

--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)