Update u2/list_ops.py

u2/list_ops.py

@@ -6,24 +6,28 @@ def append(list1, list2):
         result += [item]
     return result
 
+
 def concat(lists):
     result = []
     for sublist in lists:
         result = append(result, sublist)
     return result
 
+
 def filter(function, lst):
     result = []
-    for item in list:
+    for item in lst:
         if function(item):
             result += [item]
     return result
 
+
 def length(lst):
     result = 0
-    for item in lst:
+    for _ in lst:
-        result +=1
+        result += 1
-    return result    
+    return result
+
 
 def map(function, lst):
     result = []
@@ -31,20 +35,23 @@ def map(function, lst):
         result += [function(item)]
     return result
 
+
 def foldl(function, lst, initial):
     acc = initial
     for item in lst:
         acc = function(acc, item)
-    return acc    
-
-def foldr(function, lst, initial):
-    acc = initial
-    for acc in  lst:
-        acc = function(acc, item)
     return acc
 
+
 def reverse(lst):
     result = []
-    for item in reverse(lst):
+    for item in lst:
         result = [item] + result
-    return result
+    return result
+
+
+def foldr(function, lst, initial):
+    acc = initial
+    for item in reverse(lst):
+        acc = function(acc, item)
+    return acc