检查词典列表中是否已存在值？

I've got a Python list of dictionaries, as follows:

我有一个Python字典列表，如下所示：

a = [
    {'main_color': 'red', 'second_color':'blue'},
    {'main_color': 'yellow', 'second_color':'green'},
    {'main_color': 'yellow', 'second_color':'blue'},
]

I'd like to check whether a dictionary with a particular key/value already exists in the list, as follows:

我想检查列表中是否已存在具有特定键/值的字典，如下所示：

// is a dict with 'main_color'='red' in the list already?
// if not: add item

3 个解决方案

#1

149

Here's one way to do it:

这是一种方法：

if not any(d['main_color'] == 'red' for d in a):
    # does not exist

The part in parentheses is a generator expression that returns True for each dictionary that has the key-value pair you are looking for, otherwise False.

括号中的部分是一个生成器表达式，它为具有您要查找的键值对的每个字典返回True，否则返回False。

If the key could also be missing the above code can give you a KeyError. You can fix this by using get and providing a default value.

如果密钥也可能丢失，上面的代码可以给你一个KeyError。您可以使用get并提供默认值来解决此问题。

if not any(d.get('main_color', None) == 'red' for d in a):
    # does not exist

#2

Maybe this helps:

也许这有助于：

a = [{ 'main_color': 'red', 'second_color':'blue'},
     { 'main_color': 'yellow', 'second_color':'green'},
     { 'main_color': 'yellow', 'second_color':'blue'}]

def in_dictlist((key, value), my_dictlist):
    for this in my_dictlist:
        if this[key] == value:
            return this
    return {}

print in_dictlist(('main_color','red'), a)
print in_dictlist(('main_color','pink'), a)

#3

Perhaps a function along these lines is what you're after:

也许沿着这些方向的功能就是你所追求的：

 def add_unique_to_dict_list(dict_list, key, value):
  for d in dict_list:
     if key in d:
        return d[key]

  dict_list.append({ key: value })
  return value

#1

149