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bpo-35224: PEP 572 Implementation (#10497)

* Add tokenization of :=
- Add token to Include/token.h. Add token to documentation in Doc/library/token.rst.
- Run `./python Lib/token.py` to regenerate Lib/token.py.
- Update Parser/tokenizer.c: add case to handle `:=`.

* Add initial usage of := in grammar.

* Update Python.asdl to match the grammar updates. Regenerated Include/Python-ast.h and Python/Python-ast.c

* Update AST and compiler files in Python/ast.c and Python/compile.c. Basic functionality, this isn't scoped properly

* Regenerate Lib/symbol.py using `./python Lib/symbol.py`

* Tests - Fix failing tests in test_parser.py due to changes in token numbers for internal representation

* Tests - Add simple test for := token

* Tests - Add simple tests for named expressions using expr and suite

* Tests - Update number of levels for nested expressions to prevent stack overflow

* Update symbol table to handle NamedExpr

* Update Grammar to allow assignment expressions in if statements.
Regenerate Python/graminit.c accordingly using `make regen-grammar`

* Tests - Add additional tests for named expressions in RoundtripLegalSyntaxTestCase, based on examples and information directly from PEP 572

Note: failing tests are currently commented out (4 out of 24 tests currently fail)

* Tests - Add temporary syntax test failure tests in test_parser.py

Note: There is an outstanding TODO for this -- syntax tests need to be
moved to a different file (presumably test_syntax.py), but this is
covering what needs to be tested at the moment, and it's more convenient
to run a single test for the time being

* Add support for allowing assignment expressions as function argument annotations. Uncomment tests for these cases because they all pass now!

* Tests - Move existing syntax tests out of test_parser.py and into test_named_expressions.py. Refactor syntax tests to use unittest

* Add TargetScopeError exception to extend SyntaxError

Note: This simply creates the TargetScopeError exception, it is not yet
used anywhere

* Tests - Update tests per PEP 572

Continue refactoring test suite:
The named expression test suite now checks for any invalid cases that
throw exceptions (no longer limited to SyntaxErrors), assignment tests
to ensure that variables are properly assigned, and scope tests to
ensure that variable availability and values are correct

Note:
- There are still tests that are marked to skip, as they are not yet
implemented
- There are approximately 300 lines of the PEP that have not yet been
addressed, though these may be deferred

* Documentation - Small updates to XXX/todo comments

- Remove XXX from child description in ast.c
- Add comment with number of previously supported nested expressions for
3.7.X in test_parser.py

* Fix assert in seq_for_testlist()

* Cleanup - Denote "Not implemented -- No keyword args" on failing test case. Fix PEP8 error for blank lines at beginning of test classes in test_parser.py

* Tests - Wrap all file opens in `with...as` to ensure files are closed

* WIP: handle f(a := 1)

* Tests and Cleanup - No longer skips keyword arg test. Keyword arg test now uses a simpler test case and does not rely on an external file. Remove print statements from ast.c

* Tests - Refactor last remaining test case that relied on on external file to use a simpler test case without the dependency

* Tests - Add better description of remaning skipped tests. Add test checking scope when using assignment expression in a function argument

* Tests - Add test for nested comprehension, testing value and scope. Fix variable name in skipped comprehension scope test

* Handle restriction of LHS for named expressions - can only assign to LHS of type NAME. Specifically, restrict assignment to tuples

This adds an alternative set_context specifically for named expressions,
set_namedexpr_context. Thus, context is now set differently for standard
assignment versus assignment for named expressions in order to handle
restrictions.

* Tests - Update negative test case for assigning to lambda to match new error message. Add negative test case for assigning to tuple

* Tests - Reorder test cases to group invalid syntax cases and named assignment target errors

* Tests - Update test case for named expression in function argument - check that result and variable are set correctly

* Todo - Add todo for TargetScopeError based on Guido's comment (2b3acd3#r30472562)

* Tests - Add named expression tests for assignment operator in function arguments

Note: One of two tests are skipped, as function arguments are currently treating
an assignment expression inside of parenthesis as one child, which does
not properly catch the named expression, nor does it count arguments
properly

* Add NamedStore to expr_context. Regenerate related code with `make regen-ast`

* Add usage of NamedStore to ast_for_named_expr in ast.c. Update occurances of checking for Store to also handle NamedStore where appropriate

* Add ste_comprehension to _symtable_entry to track if the namespace is a comprehension. Initialize ste_comprehension to 0. Set set_comprehension to 1 in symtable_handle_comprehension

* s/symtable_add_def/symtable_add_def_helper. Add symtable_add_def to handle grabbing st->st_cur and passing it to symtable_add_def_helper. This now allows us to call the original code from symtable_add_def by instead calling symtable_add_def_helper with a different ste.

* Refactor symtable_record_directive to take lineno and col_offset as arguments instead of stmt_ty. This allows symtable_record_directive to be used for stmt_ty and expr_ty

* Handle elevating scope for named expressions in comprehensions.

* Handle error for usage of named expression inside a class block

* Tests - No longer skip scope tests. Add additional scope tests

* Cleanup - Update error message for named expression within a comprehension within a class. Update comments. Add assert for symtable_extend_namedexpr_scope to validate that we always find at least a ModuleScope if we don't find a Class or FunctionScope

* Cleanup - Add missing case for NamedStore in expr_context_name. Remove unused var in set_namedexpr_content

* Refactor - Consolidate set_context and set_namedexpr_context to reduce duplicated code. Special cases for named expressions are handled by checking if ctx is NamedStore

* Cleanup - Add additional use cases for ast_for_namedexpr in usage comment. Fix multiple blank lines in test_named_expressions

* Tests - Remove unnecessary test case. Renumber test case function names

* Remove TargetScopeError for now. Will add back if needed

* Cleanup - Small comment nit for consistency

* Handle positional argument check with named expression

* Add TargetScopeError exception definition. Add documentation for TargetScopeError in c-api docs. Throw TargetScopeError instead of SyntaxError when using a named expression in a comprehension within a class scope

* Increase stack size for parser by 200. This is a minimal change (approx. 5kb) and should not have an impact on any systems. Update parser test to allow 99 nested levels again

* Add TargetScopeError to exception_hierarchy.txt for test_baseexception.py_

* Tests - Major update for named expression tests, both in test_named_expressions and test_parser

- Add test for TargetScopeError
- Add tests for named expressions in comprehension scope and edge cases
- Add tests for named expressions in function arguments (declarations
and call sites)
- Reorganize tests to group them more logically

* Cleanup - Remove unnecessary comment

* Cleanup - Comment nitpicks

* Explicitly disallow assignment expressions to a name inside parentheses, e.g.: ((x) := 0)

- Add check for LHS types to detect a parenthesis then a name (see note)
- Add test for this scenario
- Update tests for changed error message for named assignment to a tuple
(also, see note)

Note: This caused issues with the previous error handling for named assignment
to a LHS that contained an expression, such as a tuple. Thus, the check
for the LHS of a named expression must be changed to be more specific if
we wish to maintain the previous error messages

* Cleanup - Wrap lines more strictly in test file

* Revert "Explicitly disallow assignment expressions to a name inside parentheses, e.g.: ((x) := 0)"

This reverts commit f153140.

* Add NEWS.d entry

* Tests - Fix error in test_pickle.test_exceptions by adding TargetScopeError to list of exceptions

* Tests - Update error message tests to reflect improved messaging convention (s/can't/cannot)

* Remove cases that cannot be reached in compile.c. Small linting update.

* Update Grammar/Tokens to add COLONEQUAL. Regenerate all files

* Update TargetScopeError PRE_INIT and POST_INIT, as this was purposefully left out when fixing rebase conflicts

* Add NamedStore back and regenerate files

* Pass along line number and end col info for named expression

* Simplify News entry

* Fix compiler warning and explicity mark fallthrough
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emilyemorehouse committed Jan 24, 2019
1 parent 1fd06f1 commit 8f59ee01be3d83d5513a9a3f654a237d77d80d9a
@@ -800,6 +800,7 @@ the variables:
single: PyExc_SystemError
single: PyExc_SystemExit
single: PyExc_TabError
single: PyExc_TargetScopeError
single: PyExc_TimeoutError
single: PyExc_TypeError
single: PyExc_UnboundLocalError
@@ -901,6 +902,8 @@ the variables:
+-----------------------------------------+---------------------------------+----------+
| :c:data:`PyExc_TabError` | :exc:`TabError` | |
+-----------------------------------------+---------------------------------+----------+
| :c:data:`PyExc_TargetScopeError` | :exc:`TargetScopeError` | |
+-----------------------------------------+---------------------------------+----------+
| :c:data:`PyExc_TimeoutError` | :exc:`TimeoutError` | |
+-----------------------------------------+---------------------------------+----------+
| :c:data:`PyExc_TypeError` | :exc:`TypeError` | |

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@@ -69,7 +69,7 @@ assert_stmt: 'assert' test [',' test]

compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt
async_stmt: 'async' (funcdef | with_stmt | for_stmt)
if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
if_stmt: 'if' namedexpr_test ':' suite ('elif' namedexpr_test ':' suite)* ['else' ':' suite]
while_stmt: 'while' test ':' suite ['else' ':' suite]
for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
try_stmt: ('try' ':' suite
@@ -83,6 +83,7 @@ with_item: test ['as' expr]
except_clause: 'except' [test ['as' NAME]]
suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT

namedexpr_test: test [':=' test]
test: or_test ['if' or_test 'else' test] | lambdef
test_nocond: or_test | lambdef_nocond
lambdef: 'lambda' [varargslist] ':' test
@@ -108,7 +109,7 @@ atom: ('(' [yield_expr|testlist_comp] ')' |
'[' [testlist_comp] ']' |
'{' [dictorsetmaker] '}' |
NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
testlist_comp: (namedexpr_test|star_expr) ( comp_for | (',' (namedexpr_test|star_expr))* [','] )
trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
subscriptlist: subscript (',' subscript)* [',']
subscript: test | [test] ':' [test] [sliceop]
@@ -134,6 +135,7 @@ arglist: argument (',' argument)* [',']
# multiple (test comp_for) arguments are blocked; keyword unpackings
# that precede iterable unpackings are blocked; etc.
argument: ( test [comp_for] |
test ':=' test |
test '=' test |
'**' test |
'*' test )
@@ -52,6 +52,7 @@ AT '@'
ATEQUAL '@='
RARROW '->'
ELLIPSIS '...'
COLONEQUAL ':='

OP
ERRORTOKEN

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@@ -108,6 +108,7 @@ PyAPI_DATA(PyObject *) PyExc_NotImplementedError;
PyAPI_DATA(PyObject *) PyExc_SyntaxError;
PyAPI_DATA(PyObject *) PyExc_IndentationError;
PyAPI_DATA(PyObject *) PyExc_TabError;
PyAPI_DATA(PyObject *) PyExc_TargetScopeError;
PyAPI_DATA(PyObject *) PyExc_ReferenceError;
PyAPI_DATA(PyObject *) PyExc_SystemError;
PyAPI_DATA(PyObject *) PyExc_SystemExit;
@@ -50,6 +50,7 @@ typedef struct _symtable_entry {
including free refs to globals */
unsigned ste_generator : 1; /* true if namespace is a generator */
unsigned ste_coroutine : 1; /* true if namespace is a coroutine */
unsigned ste_comprehension : 1; /* true if namespace is a list comprehension */
unsigned ste_varargs : 1; /* true if block has varargs */
unsigned ste_varkeywords : 1; /* true if block has varkeywords */
unsigned ste_returns_value : 1; /* true if namespace uses return with

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@@ -128,6 +128,7 @@
"SystemError",
"SystemExit",
"TabError",
"TargetScopeError",
"TypeError",
"UnboundLocalError",
"UnicodeDecodeError",
@@ -61,44 +61,45 @@
with_item = 302
except_clause = 303
suite = 304
test = 305
test_nocond = 306
lambdef = 307
lambdef_nocond = 308
or_test = 309
and_test = 310
not_test = 311
comparison = 312
comp_op = 313
star_expr = 314
expr = 315
xor_expr = 316
and_expr = 317
shift_expr = 318
arith_expr = 319
term = 320
factor = 321
power = 322
atom_expr = 323
atom = 324
testlist_comp = 325
trailer = 326
subscriptlist = 327
subscript = 328
sliceop = 329
exprlist = 330
testlist = 331
dictorsetmaker = 332
classdef = 333
arglist = 334
argument = 335
comp_iter = 336
sync_comp_for = 337
comp_for = 338
comp_if = 339
encoding_decl = 340
yield_expr = 341
yield_arg = 342
namedexpr_test = 305
test = 306
test_nocond = 307
lambdef = 308
lambdef_nocond = 309
or_test = 310
and_test = 311
not_test = 312
comparison = 313
comp_op = 314
star_expr = 315
expr = 316
xor_expr = 317
and_expr = 318
shift_expr = 319
arith_expr = 320
term = 321
factor = 322
power = 323
atom_expr = 324
atom = 325
testlist_comp = 326
trailer = 327
subscriptlist = 328
subscript = 329
sliceop = 330
exprlist = 331
testlist = 332
dictorsetmaker = 333
classdef = 334
arglist = 335
argument = 336
comp_iter = 337
sync_comp_for = 338
comp_for = 339
comp_if = 340
encoding_decl = 341
yield_expr = 342
yield_arg = 343
#--end constants--

sym_name = {}
@@ -42,6 +42,7 @@ BaseException
| +-- NotImplementedError
| +-- RecursionError
+-- SyntaxError
| +-- TargetScopeError
| +-- IndentationError
| +-- TabError
+-- SystemError

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