chore(python): add docstring for limit behavior (lancedb#800)

Closes lancedb#796

python/lancedb/query.py

@@ -260,20 +260,30 @@ def to_pydantic(self, model: Type[LanceModel]) -> List[LanceModel]:
             for row in self.to_arrow().to_pylist()
         ]
 
-    def limit(self, limit: int) -> LanceQueryBuilder:
+    def limit(self, limit: Union[int, None]) -> LanceQueryBuilder:
         """Set the maximum number of results to return.
 
         Parameters
         ----------
         limit: int
             The maximum number of results to return.
+            By default the query is limited to the first 10.
+            Call this method and pass 0, a negative value,
+            or None to remove the limit.
+            *WARNING* if you have a large dataset, removing
+            the limit can potentially result in reading a
+            large amount of data into memory and cause
+            out of memory issues.
 
         Returns
         -------
         LanceQueryBuilder
             The LanceQueryBuilder object.
         """
-        self._limit = limit
+        if limit is None or limit <= 0:
+            self._limit = None
+        else:
+            self._limit = limit
         return self
 
     def select(self, columns: list) -> LanceQueryBuilder:

python/tests/test_table.py

@@ -569,6 +569,14 @@ def test_empty_query(db):
     val = df.id.iloc[0]
     assert val == 1
 
+    table = LanceTable.create(db, "my_table2", data=[{"id": i} for i in range(100)])
+    df = table.search().select(["id"]).to_pandas()
+    assert len(df) == 10
+    df = table.search().select(["id"]).limit(None).to_pandas()
+    assert len(df) == 100
+    df = table.search().select(["id"]).limit(-1).to_pandas()
+    assert len(df) == 100
+
 
 def test_compact_cleanup(db):
     table = LanceTable.create(