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

How about a try/except block:

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 2

Here's a generalization for an arbitrary number of keys:

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")

Based on Python: Change values in dict of nested dicts using items in a list.

Answer 3

Use .get() with empty dictionaries as defaults:

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

If the Dict2 key is not present, an empty dictionary is returned, so the next chained .get() will also not find Dict3 and return an empty dictionary in turn. The in test then returns False.

The alternative is to just catch the KeyError:

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