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Commitc2ac662

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gh-131831: Implement PEP 758 – Allow except and except* expressions without parentheses (#131833)
1 parent053c285 commitc2ac662

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7 files changed

+377
-266
lines changed

7 files changed

+377
-266
lines changed

‎Doc/reference/compound_stmts.rst‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -232,6 +232,8 @@ Additional information on exceptions can be found in section :ref:`exceptions`,
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and information on using the:keyword:`raise` statement to generate exceptions
233233
may be found in section:ref:`raise`.
234234

235+
..versionchanged::next
236+
Support for optionally dropping grouping parentheses when using multiple exception types. See:pep:`758`.
235237

236238
.. _except:
237239

@@ -247,7 +249,8 @@ An expression-less :keyword:`!except` clause, if present, must be last;
247249
it matches any exception.
248250

249251
For an:keyword:`!except` clause with an expression, the
250-
expression must evaluate to an exception type or a tuple of exception types.
252+
expression must evaluate to an exception type or a tuple of exception types. Parentheses
253+
can be dropped if multiple exception types are provided and the ``as`` clause is not used.
251254
The raised exception matches an:keyword:`!except` clause whose expression evaluates
252255
to the class or a:term:`non-virtual base class <abstract base class>` of the exception object,
253256
or to a tuple that contains such a class.

‎Doc/whatsnew/3.14.rst‎

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -90,6 +90,33 @@ If you encounter :exc:`NameError`\s or pickling errors coming out of
9090
New features
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============
9292

93+
.. _whatsnew314-pep758:
94+
95+
PEP 758 – Allow except and except* expressions without parentheses
96+
------------------------------------------------------------------
97+
98+
The:keyword:`except` and:keyword:`except* <except_star>` expressions now allow
99+
parentheses to be omitted when there are multiple exception types and the ``as`` clause is not used.
100+
For example the following expressions are now valid:
101+
102+
..code-block::python
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104+
try:
105+
release_new_sleep_token_album()
106+
except AlbumNotFound, SongsTooGoodToBeReleased:
107+
print("Sorry, no new album this year.")
108+
109+
# The same applies to except* (for exception groups):
110+
try:
111+
release_new_sleep_token_album()
112+
except* AlbumNotFound, SongsTooGoodToBeReleased:
113+
print("Sorry, no new album this year.")
114+
115+
Check:pep:`758` for more details.
116+
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(Contributed by Pablo Galindo and Brett Cannon in:gh:`131831`.)
118+
119+
93120
.. _whatsnew314-pep649:
94121

95122
PEP 649: deferred evaluation of annotations

‎Grammar/python.gram‎

Lines changed: 12 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -435,14 +435,18 @@ try_stmt[stmt_ty]:
435435

436436
except_block[excepthandler_ty]:
437437
| invalid_except_stmt_indent
438-
| 'except' e=expression t=['as' z=NAME { z }] ':' b=block {
439-
_PyAST_ExceptHandler(e, (t) ? ((expr_ty) t)->v.Name.id : NULL, b, EXTRA) }
438+
| 'except' e=expressions ':' b=block {
439+
_PyAST_ExceptHandler(e, NULL, b, EXTRA) }
440+
| 'except' e=expression 'as' t=NAME ':' b=block {
441+
_PyAST_ExceptHandler(e, ((expr_ty) t)->v.Name.id, b, EXTRA) }
440442
| 'except' ':' b=block { _PyAST_ExceptHandler(NULL, NULL, b, EXTRA) }
441443
| invalid_except_stmt
442444
except_star_block[excepthandler_ty]:
443445
| invalid_except_star_stmt_indent
444-
| 'except' '*' e=expression t=['as' z=NAME { z }] ':' b=block {
445-
_PyAST_ExceptHandler(e, (t) ? ((expr_ty) t)->v.Name.id : NULL, b, EXTRA) }
446+
| 'except' '*' e=expressions ':' b=block {
447+
_PyAST_ExceptHandler(e, NULL, b, EXTRA) }
448+
| 'except' '*' e=expression 'as' t=NAME ':' b=block {
449+
_PyAST_ExceptHandler(e, ((expr_ty) t)->v.Name.id, b, EXTRA) }
446450
| invalid_except_star_stmt
447451
finally_block[asdl_stmt_seq*]:
448452
| invalid_finally_stmt
@@ -1356,16 +1360,16 @@ invalid_try_stmt:
13561360
| 'try' ':' block* except_star_block+ a='except' [expression ['as' NAME]] ':' {
13571361
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot have both 'except' and 'except*' on the same 'try'") }
13581362
invalid_except_stmt:
1359-
| 'except' a=expression ',' expressions['as' NAME] ':' {
1360-
RAISE_SYNTAX_ERROR_STARTING_FROM(a, "multiple exception types must be parenthesized") }
1363+
| 'except' a=expression ',' expressions 'as' NAME ':' {
1364+
RAISE_SYNTAX_ERROR_STARTING_FROM(a, "multiple exception types must be parenthesized when using 'as'") }
13611365
| a='except' expression ['as' NAME ] NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
13621366
| a='except' NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
13631367
| 'except' expression 'as' a=expression {
13641368
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
13651369
a, "cannot use except statement with %s", _PyPegen_get_expr_name(a)) }
13661370
invalid_except_star_stmt:
1367-
| 'except' '*' a=expression ',' expressions['as' NAME] ':' {
1368-
RAISE_SYNTAX_ERROR_STARTING_FROM(a, "multiple exception types must be parenthesized") }
1371+
| 'except' '*' a=expression ',' expressions 'as' NAME ':' {
1372+
RAISE_SYNTAX_ERROR_STARTING_FROM(a, "multiple exception types must be parenthesized when using 'as'") }
13691373
| a='except' '*' expression ['as' NAME ] NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
13701374
| a='except' '*' (NEWLINE | ':') { RAISE_SYNTAX_ERROR("expected one or more exception types") }
13711375
| 'except' '*' expression 'as' a=expression {

‎Lib/test/test_grammar.py‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1375,6 +1375,8 @@ def test_try(self):
13751375
try:1/0
13761376
except (EOFError,TypeError,ZeroDivisionError):pass
13771377
try:1/0
1378+
exceptEOFError,TypeError,ZeroDivisionError:pass
1379+
try:1/0
13781380
except (EOFError,TypeError,ZeroDivisionError)asmsg:pass
13791381
try:pass
13801382
finally:pass
@@ -1398,6 +1400,8 @@ def test_try_star(self):
13981400
try:1/0
13991401
except* (EOFError,TypeError,ZeroDivisionError):pass
14001402
try:1/0
1403+
except*EOFError,TypeError,ZeroDivisionError:pass
1404+
try:1/0
14011405
except* (EOFError,TypeError,ZeroDivisionError)asmsg:pass
14021406
try:pass
14031407
finally:pass

‎Lib/test/test_syntax.py‎

Lines changed: 5 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -1667,28 +1667,14 @@
16671667
SyntaxError: invalid syntax
16681668
16691669
Check that an multiple exception types with missing parentheses
1670-
raise a custom exception
1671-
1672-
>>> try:
1673-
... pass
1674-
... except A, B:
1675-
... pass
1676-
Traceback (most recent call last):
1677-
SyntaxError: multiple exception types must be parenthesized
1678-
1679-
>>> try:
1680-
... pass
1681-
... except A, B, C:
1682-
... pass
1683-
Traceback (most recent call last):
1684-
SyntaxError: multiple exception types must be parenthesized
1670+
raise a custom exception only when using 'as'
16851671
16861672
>>> try:
16871673
... pass
16881674
... except A, B, C as blech:
16891675
... pass
16901676
Traceback (most recent call last):
1691-
SyntaxError: multiple exception types must be parenthesized
1677+
SyntaxError: multiple exception types must be parenthesized when using 'as'
16921678
16931679
>>> try:
16941680
... pass
@@ -1697,29 +1683,15 @@
16971683
... finally:
16981684
... pass
16991685
Traceback (most recent call last):
1700-
SyntaxError: multiple exception types must be parenthesized
1686+
SyntaxError: multiple exception types must be parenthesized when using 'as'
17011687
17021688
1703-
>>> try:
1704-
... pass
1705-
... except* A, B:
1706-
... pass
1707-
Traceback (most recent call last):
1708-
SyntaxError: multiple exception types must be parenthesized
1709-
1710-
>>> try:
1711-
... pass
1712-
... except* A, B, C:
1713-
... pass
1714-
Traceback (most recent call last):
1715-
SyntaxError: multiple exception types must be parenthesized
1716-
17171689
>>> try:
17181690
... pass
17191691
... except* A, B, C as blech:
17201692
... pass
17211693
Traceback (most recent call last):
1722-
SyntaxError: multiple exception types must be parenthesized
1694+
SyntaxError: multiple exception types must be parenthesized when using 'as'
17231695
17241696
>>> try:
17251697
... pass
@@ -1728,7 +1700,7 @@
17281700
... finally:
17291701
... pass
17301702
Traceback (most recent call last):
1731-
SyntaxError: multiple exception types must be parenthesized
1703+
SyntaxError: multiple exception types must be parenthesized when using 'as'
17321704
17331705
Custom exception for 'except*' without an exception type
17341706
Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Add support for optionally dropping grouping parentheses when using multiple
2+
exception types as per:pep:`758`. Patch by Pablo Galindo

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