通过字典元素的一个键在数组中搜索该元素

Question

我正在处理学生数据，主要想做两件事。虽然我的实现可以工作，但随着数组的增长，它们往往会变得很慢：

students = [{'studentid':1001,'name':'Erick','classRoom':'SA9','ranking':23},{'studentid':1009,'name':'James','classRoom':'SA1','ranking':1}]

我想通过id来获取一个学生：

 def get_student(id):
   global students
   for student in students:
       if student['studentid'] == id:
           return student

   return False


 def update_student_rank(id, rank):
     student = get_students(id)
     if student:
        student.ranking = rank
        return student
     return False

任务很大程度上是找到一个特定的学生并对该特定的学生进行操作。当数组变大时，我注意到它确实变慢了，我想知道是否有更快的方法来找到特定的学生？

Answer 1

也许你可以试试这个：

students = [{'studentid':1001,'name':'Erick','classRoom':'SA9','ranking':23},{'studentid':1009,'name':'James','classRoom':'SA1','ranking':1}] # Original

# Pre-pocessing takes O(n)
id_lookup = dict()
for student in students:
    id_lookup[student['studentid']] = student # Assume no collision i.e. studentid is unique

# Lookup O(1)
print (id_lookup[1001]) 
# {'studentid': 1001, 'name': 'Erick', 'classRoom': 'SA9', 'ranking': 23}

做update_student_rank也很简单，因为你只需要用student = id_lookup[id]替换student = get_students(id)即可。(需要全局变量。)