Loop through all nested dictionary values?

135

for k, v in d.iteritems():
    if type(v) is dict:
        for t, c in v.iteritems():
            print "{0} : {1}".format(t, c)

I'm trying to loop through a dictionary and print out all key value pairs where the value is not a nested dictionary. If the value is a dictionary I want to go into it and print out its key value pairs...etc. Any help?

EDIT

How about this? It still only prints one thing.

def printDict(d):
    for k, v in d.iteritems():
        if type(v) is dict:
            printDict(v)
        else:
            print "{0} : {1}".format(k, v)

Full Test Case

Dictionary:

{u'xml': {u'config': {u'portstatus': {u'status': u'good'}, u'target': u'1'},
      u'port': u'11'}}

Result:

xml : {u'config': {u'portstatus': {u'status': u'good'}, u'target': u'1'}, u'port': u'11'}

This question is tagged with python dictionary

~ Asked on 2012-05-25 14:41:23

The Best Answer is


169

As said by Niklas, you need recursion, i.e. you want to define a function to print your dict, and if the value is a dict, you want to call your print function using this new dict.

Something like :

def myprint(d):
    for k, v in d.items():
        if isinstance(v, dict):
            myprint(v)
        else:
            print("{0} : {1}".format(k, v))

~ Answered on 2012-05-25 14:47:57


44

There are potential problems if you write your own recursive implementation or the iterative equivalent with stack. See this example:

    dic = {}
    dic["key1"] = {}
    dic["key1"]["key1.1"] = "value1"
    dic["key2"]  = {}
    dic["key2"]["key2.1"] = "value2"
    dic["key2"]["key2.2"] = dic["key1"]
    dic["key2"]["key2.3"] = dic

In the normal sense, nested dictionary will be a n-nary tree like data structure. But the definition doesn't exclude the possibility of a cross edge or even a back edge (thus no longer a tree). For instance, here key2.2 holds to the dictionary from key1, key2.3 points to the entire dictionary(back edge/cycle). When there is a back edge(cycle), the stack/recursion will run infinitely.

                          root<-------back edge
                        /      \           |
                     _key1   __key2__      |
                    /       /   \    \     |
               |->key1.1 key2.1 key2.2 key2.3
               |   /       |      |
               | value1  value2   |
               |                  | 
              cross edge----------|

If you print this dictionary with this implementation from Scharron

    def myprint(d):
      for k, v in d.items():
        if isinstance(v, dict):
          myprint(v)
        else:
          print "{0} : {1}".format(k, v)

You would see this error:

    RuntimeError: maximum recursion depth exceeded while calling a Python object

The same goes with the implementation from senderle.

Similarly, you get an infinite loop with this implementation from Fred Foo:

    def myprint(d):
        stack = list(d.items())
        while stack:
            k, v = stack.pop()
            if isinstance(v, dict):
                stack.extend(v.items())
            else:
                print("%s: %s" % (k, v))

However, Python actually detects cycles in nested dictionary:

    print dic
    {'key2': {'key2.1': 'value2', 'key2.3': {...}, 
       'key2.2': {'key1.1': 'value1'}}, 'key1': {'key1.1': 'value1'}}

"{...}" is where a cycle is detected.

As requested by Moondra this is a way to avoid cycles (DFS):

def myprint(d): 
    stack = list(d.items()) 
    visited = set() 
    while stack: 
        k, v = stack.pop() 
        if isinstance(v, dict): 
            if k not in visited: 
                stack.extend(v.items()) 
        else: 
            print("%s: %s" % (k, v)) 
        visited.add(k)

~ Answered on 2016-05-04 11:45:26


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