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bpo-44081: improve ast.unparse() for lambdas with no parameters #26000

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Merged
isidentical merged 1 commit into from
May 15, 2021
Merged

bpo-44081: improve ast.unparse() for lambdas with no parameters #26000

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13 changes: 8 additions & 5 deletions Lib/ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -716,9 +716,9 @@ def fill(self, text=""):
self.maybe_newline()
self.write(" " * self._indent + text)

def write(self, text):
"""Append a piece of text"""
self._source.append(text)
def write(self, *text):
"""Add new source parts"""
self._source.extend(text)

@contextmanager
def buffered(self, buffer = None):
Expand Down Expand Up @@ -1566,8 +1566,11 @@ def visit_keyword(self, node):

def visit_Lambda(self, node):
with self.require_parens(_Precedence.TEST, node):
self.write("lambda ")
self.traverse(node.args)
self.write("lambda")
with self.buffered() as buffer:
self.traverse(node.args)
if buffer:
self.write(" ", *buffer)
self.write(": ")
self.set_precedence(_Precedence.TEST, node.body)
self.traverse(node.body)
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11 changes: 11 additions & 0 deletions Lib/test/test_unparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -531,6 +531,17 @@ def test_slices(self):
self.check_src_roundtrip("a[1, 2]")
self.check_src_roundtrip("a[(1, *a)]")

def test_lambda_parameters(self):
self.check_src_roundtrip("lambda: something")
self.check_src_roundtrip("four = lambda: 2 + 2")
self.check_src_roundtrip("lambda x: x * 2")
self.check_src_roundtrip("square = lambda n: n ** 2")
self.check_src_roundtrip("lambda x, y: x + y")
self.check_src_roundtrip("add = lambda x, y: x + y")
self.check_src_roundtrip("lambda x, y, /, z, q, *, u: None")
self.check_src_roundtrip("lambda x, *y, **z: None")


class DirectoryTestCase(ASTTestCase):
"""Test roundtrip behaviour on all files in Lib and Lib/test."""

Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2021-05-09-03-26-31.bpo-44081.A-Mrto.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:func:`ast.unparse` now doesn't use redundant spaces to separate ``lambda``
and the ``:`` if there are no parameters.