[3.8] bpo-39889: Fix unparse.py for subscript. (GH-18824). (GH-18826)

(cherry picked from commit c4928fc) (cherry picked from commit 92b7278) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: miss-islington

Lib/test/test_tools/test_unparse.py

@@ -260,6 +260,20 @@ def test_dict_unpacking_in_dict(self):
  self.check_roundtrip(r"""{**{'y': 2}, 'x': 1}""")
  self.check_roundtrip(r"""{**{'y': 2}, **{'x': 1}}""")
 
+ def test_subscript(self):
+ self.check_roundtrip("a[i]")
+ self.check_roundtrip("a[i,]")
+ self.check_roundtrip("a[i, j]")
+ self.check_roundtrip("a[()]")
+ self.check_roundtrip("a[i:j]")
+ self.check_roundtrip("a[:j]")
+ self.check_roundtrip("a[i:]")
+ self.check_roundtrip("a[i:j:k]")
+ self.check_roundtrip("a[:j:k]")
+ self.check_roundtrip("a[i::k]")
+ self.check_roundtrip("a[i:j,]")
+ self.check_roundtrip("a[i:j, k]")
+
 
 class DirectoryTestCase(ASTTestCase):
  """Test roundtrip behaviour on all files in Lib and Lib/test."""

Misc/NEWS.d/next/Tools-Demos/2020-03-07-18-01-30.bpo-39889.l1czT6.rst

@@ -0,0 +1,3 @@
+Fixed ``unparse.py`` 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]``).

Tools/parser/unparse.py

@@ -562,7 +562,17 @@ def _Call(self, t):
  def _Subscript(self, t):
  self.dispatch(t.value)
  self.write("[")
- self.dispatch(t.slice)
+ if (isinstance(t.slice, ast.Index)
+ and isinstance(t.slice.value, ast.Tuple)
+ and t.slice.value.elts):
+ if len(t.slice.value.elts) == 1:
+ elt = t.slice.value.elts[0]
+ self.dispatch(elt)
+ self.write(",")
+ else:
+ interleave(lambda: self.write(", "), self.dispatch, t.slice.value.elts)
+ else:
+ self.dispatch(t.slice)
  self.write("]")
 
  def _Starred(self, t):
@@ -587,7 +597,12 @@ def _Slice(self, t):
  self.dispatch(t.step)
 
  def _ExtSlice(self, t):
- interleave(lambda: self.write(', '), self.dispatch, t.dims)
+ if len(t.dims) == 1:
+ elt = t.dims[0]
+ self.dispatch(elt)
+ self.write(",")
+ else:
+ interleave(lambda: self.write(', '), self.dispatch, t.dims)
 
  # argument
  def _arg(self, t):