Fix duplicated comma when removing a middle inline table element

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [unreleased]
 
+### Fixed
+
+- Fix invalid serialization with a duplicated comma when removing a non-edge element from a parsed inline table. ([#486](https://github.com/python-poetry/tomlkit/pull/486))
+
 ## [0.15.0] - 2026-05-10
 
 ### Changed

tests/test_items.py

@@ -931,6 +931,19 @@ def test_appending_to_parsed_inline_table_preserves_separator() -> None:
     parse(doc.as_string())
 
 
+def test_deleting_inline_table_middle_element_does_not_leave_double_separator() -> None:
+    doc = parse("a = {foo = 1, bar = 2, baz = 3}\n")
+    del doc["a"]["bar"]
+
+    # The dangling separator left by the removed key must not produce an
+    # invalid ``, ,`` sequence; the result must round-trip.
+    rendered = doc.as_string()
+    assert ", ," not in rendered
+    assert ",," not in rendered
+    assert parse(rendered) == {"a": {"foo": 1, "baz": 3}}
+    assert parse(rendered).as_string() == rendered
+
+
 def test_booleans_comparison() -> None:
     boolean = Bool(True, Trivia())
 

tomlkit/items.py

@@ -2050,6 +2050,7 @@ def as_string(self) -> str:
             ),
             None,
         )
+        pending_separator = False
         for i, (k, v) in enumerate(self._value.body):
             if k is None:
                 if isinstance(v, Whitespace) and "," in v.s:
@@ -2068,6 +2069,15 @@ def as_string(self) -> str:
                         buf += v.as_string().replace(",", "", 1)
                         continue
 
+                    if pending_separator:
+                        # A previous key was removed, leaving this comma as a
+                        # duplicate of an already emitted separator. Drop it to
+                        # avoid producing an invalid ``, ,`` sequence.
+                        buf += v.as_string().replace(",", "", 1)
+                        continue
+
+                    pending_separator = True
+
                 if i == len(self._value.body) - 1:
                     if self._new:
                         buf = buf.rstrip(", ")
@@ -2096,6 +2106,7 @@ def as_string(self) -> str:
                 f"{v_trivia_trail}"
             )
             emitted_key = True
+            pending_separator = False
             if has_explicit_commas:
                 needs_separator = True