问题:检查值是否已存在于字典列表中?

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'},
]

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

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

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:

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

回答 0

这是一种实现方法:

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,该表达式True将为每个具有您要查找的键-值对的字典返回,否则为False


如果密钥也可能丢失,则上面的代码可以给您一个KeyError。您可以使用get并提供默认值来解决此问题。如果不提供默认值,None则返回。

if not any(d.get('main_color', default_value) == 'red' for d in a):
    # does not exist

Here’s one way to do it:

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.


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 you don’t provide a default value, None is returned.

if not any(d.get('main_color', default_value) == 'red' for d in a):
    # does not exist

回答 1

也许这会有所帮助:

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)

Maybe this helps:

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)

回答 2

遵循这些原则的功能也许就是您所追求的:

 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

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

 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

回答 3

基于@Mark Byers的一个很好的答案,并紧接着@Florent问题,仅表明它也可以在具有超过2个键的dic列表中使用2个条件:

names = []
names.append({'first': 'Nil', 'last': 'Elliot', 'suffix': 'III'})
names.append({'first': 'Max', 'last': 'Sam', 'suffix': 'IX'})
names.append({'first': 'Anthony', 'last': 'Mark', 'suffix': 'IX'})

if not any(d['first'] == 'Anthony' and d['last'] == 'Mark' for d in names):

    print('Not exists!')
else:
    print('Exists!')

结果:

Exists!

Based on @Mark Byers great answer, and following @Florent question, just to indicate that it will also work with 2 conditions on list of dics with more than 2 keys:

names = []
names.append({'first': 'Nil', 'last': 'Elliot', 'suffix': 'III'})
names.append({'first': 'Max', 'last': 'Sam', 'suffix': 'IX'})
names.append({'first': 'Anthony', 'last': 'Mark', 'suffix': 'IX'})

if not any(d['first'] == 'Anthony' and d['last'] == 'Mark' for d in names):

    print('Not exists!')
else:
    print('Exists!')

Result:

Exists!

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