suggestion_list: improve readability

Replicates graphql/graphql-js@bd4deb0

Author: Cito

src/graphql/pyutils/suggestion_list.py

@@ -67,9 +67,16 @@ def measure(self, option: str):
             for j in range(1, b_len + 1):
                 cost = 0 if a[i - 1] == b[j - 1] else 1
 
-                d[i][j] = min(d[i - 1][j] + 1, d[i][j - 1] + 1, d[i - 1][j - 1] + cost)
+                current_cell = min(
+                    d[i - 1][j] + 1,  # delete
+                    d[i][j - 1] + 1,  # insert
+                    d[i - 1][j - 1] + cost,  # substitute
+                )
 
                 if i > 1 and j > 1 and a[i - 1] == b[j - 2] and a[i - 2] == b[j - 1]:
-                    d[i][j] = min(d[i][j], d[i - 2][j - 2] + 1)
+                    # transposition
+                    current_cell = min(current_cell, d[i - 2][j - 2] + 1)
+
+                d[i][j] = current_cell
 
         return d[a_len][b_len]