python字典键，指向同一字典中另一个键的值

Question

我有一个具有以下格式的python字典

data = {  'key1': 'value1',
  'key2': 'value2',
  'key3': 'value3'
}

我希望此key3值指向key1的值。 到目前为止，我尝试过的是'key3': key1['value1']或'key3': data['key1'] ，它们似乎都是无效的语法。

Answer 1

Python不像C / C ++那样支持指针，但是您可以使用列表作为引用。 要访问该值，您可以索引到列表的第一个元素。

data = {
  'key1': ['value1']
}

data['key3'] = data['key1']     #  copy the list by reference
print(f"Old: {data['key3'][0]}, {data['key3'][0] == data['key1'][0]}")

data['key1'][0] = 'new-value'   #  this will modify the value from data['key3'] as well    
print(f"New: {data['key3'][0]}, {data['key3'][0] == data['key1'][0]}")

输出：

Old: value1, True
New: new-value, True

请注意，这是假设您完全知道哪些值充当“指针”，哪些不起作用。

例如，

data = {
  'key1': ['pointer-list'],    # should act as a "pointer"
  'key2': ['normal', 'list']   # should act as a normal list
}

data['key3'] = data['key1']    # copy list by reference
data['key1'][0] = 'new-value'  # propogate new value to other references

data['key4'] = data['key2']    # oops – copy list by reference
data['key2'][0] = 'new-value'  # oops – data['key2'] should act as a normal list but
                               # the new value is propogated to data['key4'] as well

要解决此问题，请克隆或复制列表 。

import copy
data['key4'] = copy.copy(data['key2'])

# data['key4'] = copy.deepcopy(data['key2']) # if the value contains nested lists
# data['key4'] = data['key2'].copy()   # another way

Answer 2

尝试这个

data = { 'key1': 'value1', 'key2': 'value2', 'key3': 'value3' }

data['key3'] = data['key1']

print(data)

打印输出：

{'key3': 'value1', 'key2': 'value2', 'key1': 'value1'}