无法替换字典键

Question

我很困惑，为什么字典键45.0没有在cmd_gear.states()中被替换，而是在dictionary中被替换：

print 'original cmd_gear.states() = '
pprint.pprint(cmd_gear.states())

cmd_gear.states()['N'] = cmd_gear.states()[45.0]
del cmd_gear.states()[45.0]

print '\nreplaced cmd_gear.states() = '
pprint.pprint(cmd_gear.states())

dictionary = {
6.0: [[288.031, 441.971]],
45.0: [[0.211, 6.071], [34.101, 69.671], [540.021, 644.761]]}
dictionary['N'] = dictionary[45.0]
del dictionary[45.0]
print '\nreplaced dictionary'
pprint.pprint(dictionary)

以下是输出：

original cmd_gear.states() = 
{
 6.0: [[288.031, 441.971]],
 45.0: [[0.211, 6.071], [34.101, 69.671], [540.021, 644.761]]}

replaced cmd_gear.states() = 
{
 6.0: [[288.031, 441.971]],
 45.0: [[0.211, 6.071], [34.101, 69.671], [540.021, 644.761]]} # this is what confuses me!!! 45.0 should be 'N'

replaced dictionary
{
 6.0: [[288.031, 441.971]],
 'N': [[0.211, 6.071], [34.101, 69.671], [540.021, 644.761]]}

我真的很困惑为什么它不能用N代替45.0

Answer 1

正如@chepner所评论的，问题是，每次我都会得到一本新字典。必须使变量等于cmd_gear.states()，否则将无法修改它。以下是解决方案：

cmd_gear_states = cmd_gear.states()
print 'original cmd_gear_states = '
pprint.pprint(cmd_gear_states)

cmd_gear_states['N'] = cmd_gear_states[45.0]
del cmd_gear_states[45.0]

print '\nreplaced cmd_gear_states = '
pprint.pprint(cmd_gear_states)