python - Check nested dictionary values?

Question

For a large list of nested dictionaries, I want to check if they contain or not a key. Each of them may or may not have one of the nested dictionaries, so if I loop this search through all of them raises an error:

for Dict1 in DictionariesList:
     if "Dict4" in Dict1['Dict2']['Dict3']:
         print "Yes"

My solution so far is:

for Dict1 in DictionariesList:    
    if "Dict2" in Dict1:
        if "Dict3" in Dict1['Dict2']:
            if "Dict4" in Dict1['Dict2']['Dict3']:
                print "Yes"

But this is a headache, ugly, and probably not very resources effective. Which would be the correct way to do this in the first type fashion, but without raising an error when the dictionary doesnt exist?

Answer 1

使用.get()空字典作为默认值：

if 'Dict4' in Dict1.get('Dict2', {}).get('Dict3', {}):
    print "Yes"

如果Dict2键不存在，则返回一个空字典，因此下一个链式.get()也将找不到Dict3并依次返回一个空字典。然后in测试返回False。

另一种方法是抓住KeyError：

try:
    if 'Dict4' in Dict1['Dict2']['Dict3']:
        print "Yes"
except KeyError:
    print "Definitely no"

Answer 2

try/except 块怎么样：

for Dict1 in DictionariesList:
    try:
        if 'Dict4' in Dict1['Dict2']['Dict3']:
            print 'Yes'
    except KeyError:
        continue # I just chose to continue.  You can do anything here though

Answer 3

这是任意数量的键的概括：

for Dict1 in DictionariesList:
    try: # try to get the value
        reduce(dict.__getitem__, ["Dict2", "Dict3", "Dict4"], Dict1)
    except KeyError: # failed
        continue # try the next dict
    else: # success
        print("Yes")

基于Python：使用列表中的项目更改嵌套字典的字典中的值。