simplify slicing logic

Author: miguelgrinberg

elasticsearch_dsl/search_base.py

@@ -363,13 +363,22 @@ def __getitem__(self, n):
         # Elasticsearch won't get all results so we default to size: 10 if
         # stop not given.
         old_from = s._extra.get("from", 0)
-        old_to = old_from + s._extra.get(
-            "size", slice_stop or (slice_start or old_from) + 10
-        )
+        if "size" in s._extra:
+            old_to = old_from + s._extra["size"]
+        elif slice_stop is not None:
+            # inherit a size from the given slice
+            old_to = old_from + slice_stop
+        elif slice_start is not None:
+            # assume a default size of 10 from the given slice start
+            old_to = old_from + slice_start + 10
+        else:
+            # with no other information, the default size is 10
+            old_to = old_from + 10
         new_from = old_from + (slice_start or 0)
-        new_to = (
-            min(old_to, old_from + slice_stop) if slice_stop is not None else old_to
-        )
+        if slice_stop is not None:
+            new_to = min(old_to, old_from + slice_stop)
+        else:
+            new_to = old_to
         s._extra["from"] = new_from
         s._extra["size"] = max(0, new_to - new_from)
         return s

tests/_async/test_search.py

@@ -365,6 +365,13 @@ def test_slice():
     assert {"from": 10, "size": 0} == s[:5][10:].to_dict()
     assert {"from": 12, "size": 0} == s[:5][10:][2:].to_dict()
     assert {"from": 15, "size": 0} == s[10:][:5][5:].to_dict()
+    assert {"from": 0, "size": 10} == s[:].to_dict()
+    with raises(ValueError):
+        s[-1:]
+    with raises(ValueError):
+        s[4:-1]
+    with raises(ValueError):
+        s[-3:-2]
 
 
 def test_index():
@@ -373,6 +380,8 @@ def test_index():
     assert {"from": 3, "size": 1} == s[3][0].to_dict()
     assert {"from": 8, "size": 0} == s[3][5].to_dict()
     assert {"from": 4, "size": 1} == s[3:10][1].to_dict()
+    with raises(ValueError):
+        s[-3]
 
 
 def test_search_to_dict():

tests/_sync/test_search.py

@@ -365,6 +365,12 @@ def test_slice():
     assert {"from": 10, "size": 0} == s[:5][10:].to_dict()
     assert {"from": 12, "size": 0} == s[:5][10:][2:].to_dict()
     assert {"from": 15, "size": 0} == s[10:][:5][5:].to_dict()
+    with raises(ValueError):
+        s[-1:]
+    with raises(ValueError):
+        s[4:-1]
+    with raises(ValueError):
+        s[-3:-2]
 
 
 def test_index():
@@ -373,6 +379,8 @@ def test_index():
     assert {"from": 3, "size": 1} == s[3][0].to_dict()
     assert {"from": 8, "size": 0} == s[3][5].to_dict()
     assert {"from": 4, "size": 1} == s[3:10][1].to_dict()
+    with raises(ValueError):
+        s[-3]
 
 
 def test_search_to_dict():