Make or_list function more readable

Replicates graphql/graphql-js@7a27ef1

Author: Cito

graphql/pyutils/or_list.py

@@ -9,8 +9,12 @@
 def or_list(items: Sequence[str]) -> Optional[str]:
     """Given [A, B, C] return 'A, B, or C'."""
     if not items:
-        raise TypeError("List must not be empty")
+        raise ValueError
+
     if len(items) == 1:
         return items[0]
-    selected = items[:MAX_LENGTH]
-    return ", ".join(selected[:-1]) + " or " + selected[-1]
+    if len(items) == 2:
+        return items[0] + " or " + items[1]
+
+    *selected, last_item = items[:MAX_LENGTH]
+    return ", ".join(selected) + " or " + last_item

tests/pyutils/test_or_list.py

@@ -5,7 +5,7 @@
 
 def describe_or_list():
     def returns_none_for_empty_list():
-        with raises(TypeError):
+        with raises(ValueError):
             or_list([])
 
     def prints_list_with_one_item():

tests/pyutils/test_quoted_or_list.py

@@ -5,7 +5,7 @@
 
 def describe_quoted_or_list():
     def does_not_accept_an_empty_list():
-        with raises(TypeError):
+        with raises(ValueError):
             quoted_or_list([])
 
     def returns_single_quoted_item():