这里是一种方法:

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

括号中的部分是一个生成器表达式，对于具有要查找的键值对的每个词典，返回True，否则返回False.

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.

如果密钥也可能丢失，则上面的代码可以为您提供KeyError.您可以使用get并提供默认值来解决此问题.

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.

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