Suppose I have a python dictionary , many nests.

Question

If a lot of nested dictionarys, I am trying to find a certain key.

this key is called "fruit". But it's nested inside somewhere. How do I find the value of this key?

Answer 1

(Making some wild guesses about your data structure...)

Do it recursively:

def findkey(d, key):
    if key in d: return d[key]
    for k,subdict in d.iteritems():
        val = findkey(subdict, key)
        if val: return val

Answer 2

Just traverse the dictionary and check for the keys (note the comment in the bottom about the "not found" value).

def find_key_recursive(d, key):
  if key in d:
    return d[key]
  for k, v in d.iteritems():
    if type(v) is dict: # Only recurse if we hit a dict value
      value = find_key_recursive(v, key)
      if value:
        return value
  # You may want to return something else than the implicit None here (and change the tests above) if None is an expected value

Answer 3

@Håvard's recursive solution is probably going to be OK... unless the level of nesting is too high, and then you get a RuntimeError: maximum recursion depth exceeded. To remedy that, you can use the usual technique for recursion removal: keep your own stack of items to examine (as a list that's under your control). I.e.:

def find_key_nonrecursive(adict, key):
  stack = [adict]
  while stack:
    d = stack.pop()
    if key in d:
      return d[key]
    for k, v in d.iteritems():
      if isinstance(v, dict):
        stack.append(v)

The logic here is quite close to the recursive answer (except for checking for dict in the right way;-), with the obvious exception that the recursive calls are replaced with a while loop and .pop and .append operations on the explicit-stack list, stack.