Try something

2015/day 5/P2/string.py

@@ -1,14 +1,17 @@
 strings = open("input.txt").read().split("\n")[:-1]
 nice = 0
 for i in strings:
+    pair = False
     double = False
     for j in range(len(i)-1):
+        if not pair:
             if i.count(f"{i[j]}{i[j+1]}") >= 2 and f"{i[j]}{i[j]}{i[j]}" not in i:
-            double = True
-            break
-    for j in range(len(i)):
+                pair = True
+        if not double:
             f2 = i.find(i[j], j+1)
-        if f2-j == 2 and double:
+            if f2-j == 2:
+                double = True
+        if pair and double:
             nice+=1
             break
 print(nice)