update whatsnew

Author: aram-cedarwood

doc/source/whatsnew/v3.0.0.rst

@@ -645,6 +645,7 @@ Other
 - Bug in :meth:`DataFrame.apply` where passing ``engine="numba"`` ignored ``args`` passed to the applied function (:issue:`58712`)
 - Bug in :meth:`DataFrame.eval` and :meth:`DataFrame.query` which caused an exception when using NumPy attributes via ``@`` notation, e.g., ``df.eval("@np.floor(a)")``. (:issue:`58041`)
 - Bug in :meth:`DataFrame.eval` and :meth:`DataFrame.query` which did not allow to use ``tan`` function. (:issue:`55091`)
+- Bug in :meth:`DataFrame.query` which raised a ``KeyError`` when the expression contained column names with  characters like ``#``. (:issue:`59285`)
 - Bug in :meth:`DataFrame.sort_index` when passing ``axis="columns"`` and ``ignore_index=True`` and ``ascending=False`` not returning a :class:`RangeIndex` columns (:issue:`57293`)
 - Bug in :meth:`DataFrame.transform` that was returning the wrong order unless the index was monotonically increasing. (:issue:`57069`)
 - Bug in :meth:`DataFrame.where` where using a non-bool type array in the function would return a ``ValueError`` instead of a ``TypeError`` (:issue:`56330`)

pandas/core/frame.py

@@ -4627,7 +4627,7 @@ def query(self, expr: str, *, inplace: bool = False, **kwargs) -> DataFrame | No
             column_name_to_escaped = {
                 col: urllib.parse.quote(col) for col in self.columns
             }
-            # Odd-number indexes are column names
+            # A `token` with an odd-number index is a column name
             escaped_expr = "`".join(
                 (column_name_to_escaped.get(token, token) if (i % 2) else token)
                 for i, token in enumerate(expr.split("`"))