Ignore failure to delete list comp variables

When iterating over a generator expression `gen` in a list comprehension
`[for x in gen]`, the local variable `x` holds the value of each
generated expression. When the list comprehension is done being
evaluated, the local variable `x` needs to be deleted. This was already
being done. If, however, `gen` is empty, `x` is never defined, and so
deleting it causes an error. This patch adds a check to ignore that
error.

custom_components/pyscript/eval.py

@@ -1753,7 +1753,12 @@ async def loopvar_scope_restore(self, var_names, save_vars):
             if var_name in save_vars:
                 self.sym_table[var_name] = save_vars[var_name]
             else:
-                del self.sym_table[var_name]
+                try:
+                    del self.sym_table[var_name]
+                except KeyError as e:
+                    # If the iterator was empty, the loop variables were never
+                    # assigned to, so deleting them will fail.
+                    pass
 
     async def listcomp_loop(self, generators, elt):
         """Recursive list comprehension."""

tests/test_unit_eval.py

@@ -81,6 +81,8 @@
     ["kw = {'x': 1, 'y': 5}; kw2 = {'z': 10}; {**kw, **kw2}", {"x": 1, "y": 5, "z": 10}],
     ["[*iter([1, 2, 3])]", [1, 2, 3]],
     ["{*iter([1, 2, 3])}", {1, 2, 3}],
+    ["[x for x in []]", []],
+    ["[x for x in [] if x]", []],
     ["if 1: x = 10\nelse: x = 20\nx", 10],
     ["if 0: x = 10\nelse: x = 20\nx", 20],
     ["i = 0\nwhile i < 5: i += 1\ni", 5],