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bpo-39889: Fix ast.unparse() for subscript. #18824

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Merged
serhiy-storchaka merged 1 commit into from
Mar 7, 2020
Merged

bpo-39889: Fix ast.unparse() for subscript. #18824

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19 changes: 17 additions & 2 deletions Lib/ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1261,7 +1261,17 @@ def visit_Subscript(self, node):
self.set_precedence(_Precedence.ATOM, node.value)
self.traverse(node.value)
with self.delimit("[", "]"):
self.traverse(node.slice)
if (isinstance(node.slice, Index)
and isinstance(node.slice.value, Tuple)
and node.slice.value.elts):
if len(node.slice.value.elts) == 1:
elt = node.slice.value.elts[0]
self.traverse(elt)
self.write(",")
else:
self.interleave(lambda: self.write(", "), self.traverse, node.slice.value.elts)
else:
self.traverse(node.slice)

def visit_Starred(self, node):
self.write("*")
Expand All @@ -1286,7 +1296,12 @@ def visit_Slice(self, node):
self.traverse(node.step)

def visit_ExtSlice(self, node):
self.interleave(lambda: self.write(", "), self.traverse, node.dims)
if len(node.dims) == 1:
elt = node.dims[0]
self.traverse(elt)
self.write(",")
else:
self.interleave(lambda: self.write(", "), self.traverse, node.dims)

def visit_arg(self, node):
self.write(node.arg)
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14 changes: 14 additions & 0 deletions Lib/test/test_unparse.py
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Expand Up @@ -344,6 +344,20 @@ def test_simple_expressions_parens(self):
self.check_src_roundtrip("call((yield x))")
self.check_src_roundtrip("return x + (yield x)")

def test_subscript(self):
self.check_src_roundtrip("a[i]")
self.check_src_roundtrip("a[i,]")
self.check_src_roundtrip("a[i, j]")
self.check_src_roundtrip("a[()]")
self.check_src_roundtrip("a[i:j]")
self.check_src_roundtrip("a[:j]")
self.check_src_roundtrip("a[i:]")
self.check_src_roundtrip("a[i:j:k]")
self.check_src_roundtrip("a[:j:k]")
self.check_src_roundtrip("a[i::k]")
self.check_src_roundtrip("a[i:j,]")
self.check_src_roundtrip("a[i:j, k]")

def test_docstrings(self):
docstrings = (
'"""simple doc string"""',
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2020-03-07-16-44-51.bpo-39889.3RYqeX.rst
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@@ -0,0 +1,3 @@
Fixed :func:`ast.unparse` for extended slices containing a single element
(e.g. ``a[i:j,]``). Remove redundant tuples when index with a tuple (e.g.
``a[i, j]``).