如何在Python中更新字典的值，让用户选择要更新的键和新值？

Question

我正在尝试写一个程序，让我和我哥哥可以输入和编辑我们足球比赛的阵容信息，以便比较球队和管理球员等等。这是我尝试的第一个“大”项目。

我在一个字典里面有一个嵌套的字典，我能让用户创建这些字典。但是当我想让用户（通过输入）回去编辑这些字典时，我就卡住了。下面我尝试写了一个简化版的代码，觉得和我的错误有关。如果需要我提供完整的代码，请告诉我。

player1 = {'stat1' : A, 'stat2' : 2, 'stat3' : 3} #existing players are the dictionaries 
player2 = {'stat1' : A, 'stat2' : 2, 'stat3' : 3} # containing the name of stat and its value
position1 = {'player1' : player1} # in each position the string (name of player) is the key and
position2 = {'player2' : player2} # the similarly named dict containing the statisics is the value
position = raw_input('which position? ') # user chooses which position to edit
if position == 'position1':
  print position1 # shows user what players are available to choose from in that position
  player = raw_input('which player? ') #user chooses player from available at that position
  if player == player1:
    print player # shows user the current stats for the player they chose
    edit_query = raw_input('Do you need to edit one or more of these stats? ')
    editloop = 0
    while editloop < 1: # while loop to allow multiple stats editing
      if edit_query == 'yes': 
        stat_to_edit = raw_input('Which stat? (If you are done type "done") ')
          if stat_to_edit == 'done': #end while loop for stat editing
            editloop = editloop +1
          else:
            new_value = raw_input('new_value: ') #user inserts new value

# up to here everything is working. 
# in the following line, player should give the name of the
# dictionary to change (either player1 or player2) 
# stat_to_edit should give the key where the matching value is to be changed
# and new_value should update the stastic
# however I get TypeError 'str' object does not support item assignment

            player[stat_to_edit] = new_value #update statistic
      else:  # end loop if no stat editing is wanted
        fooedit = fooedit + 1

当然，当我说“应该给...”的时候，我是想说“我希望它给...”。

总之，我想让用户选择要编辑的球员，选择要编辑的统计数据，然后选择新的值。

Answer 1

问题出在这一行之后：

player = raw_input('which player? ')

此时，player 变成了一个字符串，里面包含了用户输入的内容，而不是像 player1 那样的字典。这就解释了为什么 Python 无法正确赋值给它的部分。你可以这样写：

player = raw_input('which player? ')
if player == 'player1': # these are strings!
  current_player = player1 # this is dictionary!
  ....
  current_player[...] = ... # change the dictionary

另外要注意，Python 在给一个名字赋值时，通常并不会复制对象，而只是为同一个现有对象添加另一个名字。看看这个例子（来自 Python 控制台）：

>>> a = {'1': 1}
>>> a
{'1': 1}
>>> b = a
>>> b
{'1': 1}
>>> b['1'] = 2
>>> b
{'1': 2}
>>> a
{'1': 2}
>>>