On 11/10/2020 17:20, haael wrote:
Very often I use the following construction (especially in operators):
try:
something
except SomeError:
try:
something_else
except AnotherError:
try:
something_completely_different
except Whatever:
return NotImplemented
I propose a construction to simplify the staircase hierarchy of
exception handlers:
try:
something
except SomeError try:
something_else
except AnotherError try:
something_completely_different
except Whatever:
return NotImplemented
This would be somewhat analogous to `else if` blocks.
This pattern is very common in operator implementations. And this
proposal could simplify it a bit.
haael
I sometimes encounter these somewhat analogous situations:
(a) To accomplish a goal takes several stages; failure at any stage
means the whole attempt must be abandoned.
(b) I attempt various ways to accomplish a goal; success in any way
means that the others need not be attempted.
which, in common with the OP's example, can lead to indefinite nesting
levels.
One workaround I sometimes use is a pseudo-loop which is executed once
only; whenever the process can be abandoned, I `break` out of the
"loop". It ain't particularly elegant, but it works. Applying to the
OP's example we might have:
for _ in '1': # pseudo-loop
# NB One gotcha is to write a pseudo-loop with something like "while True"
# and then forget to put in a final `break'.
try:
something
break
except SomeError:
pass
try:
something_else
break
except AnotherError:
pass
try:
something_completely_different
except Whatever:
return NotImplemented
If convenient (it isn't always) the code can be hived off to a function
and the `break's replaced by `return's. If this applied to the OP's
example it could maybe be written:
try:
something
return <some result>
except SomeError:
pass
try:
something_else
return <some other result>
except AnotherError:
pass
try:
something_completely_different
return <completely different result>
except Whatever:
return NotImplemented
or (more verbose but cleaner if the `return` statements might raise an
exception (including NameError for a misspelt variable name)):
try:
something
except SomeError:
pass
else:
return <some result>
try:
something_else
except AnotherError:
pass
else:
return <some other result>
try:
something_completely_different
except Whatever:
return NotImplemented
else:
return <completely different result>
I sometimes wish that Python provided nicer syntax for writing a
"pseudo-loop", but I guess it's not an urgent need. And I guess the
same applies to the OP's suggestion. So I'm -0.8 on it.
Best wishes
Rob Cliffe
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