bpo-43521: Allow ast.unparse with empty sets and NaN (GH-24897)
Automerge-Triggered-By: GH:pablogsal
diff --git a/Lib/ast.py b/Lib/ast.py
index 03ae2ec..e46ab43 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -1199,8 +1199,13 @@ def _write_docstring(self, node):
def _write_constant(self, value):
if isinstance(value, (float, complex)):
- # Substitute overflowing decimal literal for AST infinities.
- self.write(repr(value).replace("inf", _INFSTR))
+ # Substitute overflowing decimal literal for AST infinities,
+ # and inf - inf for NaNs.
+ self.write(
+ repr(value)
+ .replace("inf", _INFSTR)
+ .replace("nan", f"({_INFSTR}-{_INFSTR})")
+ )
elif self._avoid_backslashes and isinstance(value, str):
self._write_str_avoiding_backslashes(value)
else:
@@ -1273,10 +1278,13 @@ def visit_IfExp(self, node):
self.traverse(node.orelse)
def visit_Set(self, node):
- if not node.elts:
- raise ValueError("Set node should have at least one item")
- with self.delimit("{", "}"):
- self.interleave(lambda: self.write(", "), self.traverse, node.elts)
+ if node.elts:
+ with self.delimit("{", "}"):
+ self.interleave(lambda: self.write(", "), self.traverse, node.elts)
+ else:
+ # `{}` would be interpreted as a dictionary literal, and
+ # `set` might be shadowed. Thus:
+ self.write('{*()}')
def visit_Dict(self, node):
def write_key_value_pair(k, v):
diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
index c7c8613..ce03272 100644
--- a/Lib/test/test_unparse.py
+++ b/Lib/test/test_unparse.py
@@ -199,6 +199,12 @@ def test_huge_float(self):
self.check_ast_roundtrip("1e1000j")
self.check_ast_roundtrip("-1e1000j")
+ def test_nan(self):
+ self.assertASTEqual(
+ ast.parse(ast.unparse(ast.Constant(value=float('nan')))),
+ ast.parse('1e1000 - 1e1000')
+ )
+
def test_min_int(self):
self.check_ast_roundtrip(str(-(2 ** 31)))
self.check_ast_roundtrip(str(-(2 ** 63)))
@@ -252,6 +258,12 @@ def test_annotations(self):
def test_set_literal(self):
self.check_ast_roundtrip("{'a', 'b', 'c'}")
+ def test_empty_set(self):
+ self.assertASTEqual(
+ ast.parse(ast.unparse(ast.Set(elts=[]))),
+ ast.parse('{*()}')
+ )
+
def test_set_comprehension(self):
self.check_ast_roundtrip("{x for x in range(5)}")
@@ -326,9 +338,6 @@ def test_invalid_fstring_conversion(self):
def test_invalid_fstring_backslash(self):
self.check_invalid(ast.FormattedValue(value=ast.Constant(value="\\\\")))
- def test_invalid_set(self):
- self.check_invalid(ast.Set(elts=[]))
-
def test_invalid_yield_from(self):
self.check_invalid(ast.YieldFrom(value=None))