On 7/10/2020 1:21 AM, Stefano Borini wrote:
Just my 2 cents, I find it kind of annoying that the whole structure
requires two levels of indentation to actually reach the operational
code.
This would be a first in python.
I would prefer an option akin to if elif elif else where each block is
only one level deep.
Me too.
That would also sidestep the dilemma of whether else: (if implemented)
should be indented like case: or like match: because they would be the same.
match:
t
case ("rect", real, imag):
return complex(real, imag)
case ("polar", r, phi):
return complex( r* cos(phi), r*sin(phi)
else:
return None
but it does make the match: block not a statement group, which was
disturbing to some.
On the other hand, this has a correspondence to:
try:
throw expression
except (type of expression) as exc1:
blah blah1
except (another type) as exc2:
blah blah2
else:
blah blah3
In fact, one _could_ wrap this whole feature into the try: syntax... the
match statement would be tried, and the cases would be special types of
exception handlers:
try:
match expression
case ("rect", real, imag):
return complex(real, imag)
case ("polar", r, phi):
return complex( r* cos(phi), r*sin(phi)
else:
return None
If the expression could fail to be calculated, one could have a mix of
except clauses also to catch those, rather than needing to wrap the
whole match expression in a separate try to handle that case [making the
nesting even deeper :( ]
There might even be a use for using case clauses to extend "normal"
exception handling, where the exception object could be tested for its
content as well as its class to have different handling.
try:
raise Exception("msg", 35, things)
case Exception( x, "widgets"):
blah blah 1
case Exception( x, "characters"):
blah blah 2
else:
blah blah 3
In this not-fully-thought-through scenario, maybe the keyword match
isn't even needed: "raise expression" could do the job, or they could be
aliases to signify intent.
In other words, a match expression would always "fail". The only
mismatch here is that it points out the difference between try-else and
match-else: try-else is executed if there is no failure, but if match
always fails, else would never be appropriate, and case _: would be.
In any case, it does seem there is a strong correlation between match
processing and try processing, that I didn't see during other
discussions of the possible structural similarities. "match 3 / 0:"
would clearly need to be wrapped in a try:
try:
match x / y:
case 43:
print("wow, it is 43")
case 22:
print("22 seemed less likely than 43 for some reason")
case _:
print("You get what you get")
except ZeroDivisionError as exc:
print(f"But sometimes you get an exception {exc}")
or:
try:
raise x / y
case 43:
print("wow, it is 43")
case 22:
print("22 seemed less likely than 43 for some reason")
case exc := ZeroDivisionError:
print(f"But sometimes you get an exception: {exc}")
case _:
print("You get what you get")
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