Finding a key inside a nested dictionary with Python

Ditionary:

data =
"president":
"name": "Zaphod Beeblebrox",
"species": "Betelgeusian"




What I'd like to do is return if a key named "name" exists.

if 'president' in data and 'name' in data['president']:
print("found")


This works fine but only if I have pre knowledge of the dictionary's structure. Is there a way of knowing if there's a subkey called "name" recursively? I only found how to do this for the top level.

3 Answers
3

You can do a recursive search:

data =
"president":
"name": "Zaphod Beeblebrox",
"species": "Betelgeusian"



def r_find(target, key):
if key in target:
return True
else:
for k, v in target.items():
if isinstance(v, dict):
if r_find(v, key):
return True
return False


print(r_find(data, "name"))
print(r_find(data, "species"))
print(r_find(data, "no-name"))


Output

True
True
False


You can define a recursive generator with try / except:

try

except

def recursive_keys(d):
for k, v in d.items():
try:
yield from recursive_keys(v)
except AttributeError:
yield k

'name' in set(recursive_keys(data)) # True


If you prefer, you can use isinstance instead:

isinstance

def recursive_keys(d):
for k, v in d.items():
if isinstance(v, dict):
yield from recursive_keys(v)
else:
yield k


This is relatively expensive, since you are first creating a set of all keys before checking if an item exists in the set. As per @pault's comment, you can use:

set

set

any(x == 'name' for x in recursive_keys(data))


For a lazy solution without generators, see @DanielMesejo's solution. This may be more efficient since it avoids expensive __next__ calls.

__next__

in

any(x == 'name' for x in recursive_keys(data))

True

any

A bit of a hacky non-traditional way would be to convert your dict to a string using json.dumps. Then you can search for the key as in the string.

dict

json.dumps

For example:

import json

def find_key(d, key):
if not isinstance(d, dict):
return False
else:
return '"'+key+'": ' in json.dumps(d)

print(find_key(data, 'name'))
#True


One limitation is that this won't work if you can have "name: " inside one of your values.

"name: "

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