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bpo-36541: lib2to3: Support named assignment expressions by thatch · Pull Request #12702 · python/cpython · GitHub

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bpo-36541: lib2to3: Support named assignment expressions #12702

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Merged
gpshead merged 1 commit into from
Apr 2, 2020
Conversation 12 Commits 1 Checks 0 Files changed
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bpo-36541: lib2to3: Support named assignment expressions #12702

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10 changes: 6 additions & 4 deletions Lib/lib2to3/Grammar.txt
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Expand Up @@ -67,8 +67,8 @@ 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]
while_stmt: 'while' test ':' suite ['else' ':' suite]
if_stmt: 'if' namedexpr_test ':' suite ('elif' namedexpr_test ':' suite)* ['else' ':' suite]
while_stmt: 'while' namedexpr_test ':' suite ['else' ':' suite]
for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
try_stmt: ('try' ':' suite
((except_clause ':' suite)+
Expand All @@ -91,6 +91,7 @@ testlist_safe: old_test [(',' old_test)+ [',']]
old_test: or_test | old_lambdef
old_lambdef: 'lambda' [varargslist] ':' old_test

namedexpr_test: test [':=' test]
test: or_test ['if' or_test 'else' test] | lambdef
or_test: and_test ('or' and_test)*
and_test: not_test ('and' not_test)*
Expand All @@ -111,8 +112,8 @@ atom: ('(' [yield_expr|testlist_gexp] ')' |
'{' [dictsetmaker] '}' |
'`' testlist1 '`' |
NAME | NUMBER | STRING+ | '.' '.' '.')
listmaker: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
testlist_gexp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
listmaker: (namedexpr_test|star_expr) ( comp_for | (',' (namedexpr_test|star_expr))* [','] )
testlist_gexp: (namedexpr_test|star_expr) ( comp_for | (',' (namedexpr_test|star_expr))* [','] )
lambdef: 'lambda' [varargslist] ':' test
trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
subscriptlist: subscript (',' subscript)* [',']
Expand All @@ -137,6 +138,7 @@ 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 )
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1 change: 1 addition & 0 deletions Lib/lib2to3/pgen2/grammar.py
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Expand Up @@ -178,6 +178,7 @@ def report(self):
// DOUBLESLASH
//= DOUBLESLASHEQUAL
-> RARROW
:= COLONEQUAL
"""

opmap = {}
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3 changes: 2 additions & 1 deletion Lib/lib2to3/pgen2/token.py
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Expand Up @@ -65,7 +65,8 @@
AWAIT = 56
ASYNC = 57
ERRORTOKEN = 58
N_TOKENS = 59
COLONEQUAL = 59
N_TOKENS = 60
NT_OFFSET = 256
#--end constants--

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2 changes: 1 addition & 1 deletion Lib/lib2to3/pgen2/tokenize.py
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Expand Up @@ -93,7 +93,7 @@ def _combinations(*l):
r"~")

Bracket = '[][(){}]'
Special = group(r'\r?\n', r'[:;.,`@]')
Special = group(r'\r?\n', r':=', r'[:;.,`@]')
Funny = group(Operator, Bracket, Special)

PlainToken = group(Number, Funny, String, Name)
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15 changes: 15 additions & 0 deletions Lib/lib2to3/tests/test_parser.py
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Expand Up @@ -629,6 +629,21 @@ def test_multiline_str_literals(self):
self.validate(s)


class TestNamedAssignments(GrammarTest):

def test_named_assignment_if(self):
driver.parse_string("if f := x(): pass\n")

def test_named_assignment_while(self):
driver.parse_string("while f := x(): pass\n")

def test_named_assignment_generator(self):
driver.parse_string("any((lastNum := num) == 1 for num in [1, 2, 3])\n")

def test_named_assignment_listcomp(self):
driver.parse_string("[(lastNum := num) == 1 for num in [1, 2, 3]]\n")


class TestPickleableException(unittest.TestCase):
def test_ParseError(self):
err = ParseError('msg', 2, None, (1, 'context'))
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2019-06-18-19-38-27.bpo-36541.XI8mi1.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
lib2to3 now recognizes named assignment expressions (the walrus operator,
``:=``)
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