Loop through all nested dictionary values

Question

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

User · Answer

I am using the following code to print all the values of a nested dictionary, taking into account where the value could be a list containing dictionaries. This was useful to me when parsing a JSON file into a dictionary and needing to quickly check whether any of its values are None.

    d = {
            "user": 10,
            "time": "2017-03-15T14:02:49.301000",
            "metadata": [
                {"foo": "bar"},
                "some_string"
            ]
        }


    def print_nested(d):
        if isinstance(d, dict):
            for k, v in d.items():
                print_nested(v)
        elif hasattr(d, '__iter__') and not isinstance(d, str):
            for item in d:
                print_nested(item)
        elif isinstance(d, str):
            print(d)

        else:
            print(d)

    print_nested(d)

Output:

    10
    2017-03-15T14:02:49.301000
    bar
    some_string

User · Answer

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

User · Answer

Your question already has been answered well  but I recommend using isinstance d  collections Mapping  instead of isinstance d  dict   It works for dict    collections OrderedDict    and collections UserDict    The generally correct version is  def myprint d       for k  v in d items            if isinstance v  collections Mapping               myprint v          else              print  quot  0     1  quot  format k  v

User · Answer

These answers work for only 2 levels of sub-dictionaries  For more try this   nested dict     dictA     key 1    value 1    key 1A    value 1A   key 1Asub1     Asub1    Asub1 val    sub subA1     sub subA1 key   sub subA1 val                       dictB     key 2    value 2                    1    key 3    value 3    key 3A    value 3A     def print dict dictionary       dictionary array    dictionary      for sub dictionary in dictionary array          if type sub dictionary  is dict              for key  value in sub dictionary items                    print  key    key                  print  value   value                  if type value  is dict                      dictionary array append value     print dict nested dict

User · Answer

Here is pythonic way to do it  This function will allow you to loop through key-value pair in all the levels  It does not save the whole thing to the memory but rather walks through the dict as you loop through it  def recursive items dictionary       for key  value in dictionary items            if type value  is dict              yield  key  value              yield from recursive items value          else              yield  key  value   a     a    1   1  2  3  4   2   5  6     for key  value in recursive items a       print key  value    Prints  a  1   1  2  3  4   2   5  6   1  1  2  3  4  1 2 3 4 2  5  6  5 6

User · Answer

Since a dict is iterable  you can apply the classic nested container iterable formula to this problem with only a couple of minor changes  Here s a Python 2 version  see below for 3    import collections def nested dict iter nested       for key  value in nested iteritems            if isinstance value  collections Mapping               for inner key  inner value in nested dict iter value                   yield inner key  inner value         else              yield key  value   Test   list nested dict iter   a    b    c  1   d  2                                 e    f  3   g  4                             h    i  5   j  6       output     g   4     f   3     c   1     d   2     i   5     j   6     In Python 2  It might be possible to create a custom Mapping that qualifies as a Mapping but doesn t contain iteritems  in which case this will fail  The docs don t indicate that iteritems is required for a Mapping  on the other hand  the source gives Mapping types an iteritems method  So for custom Mappings  inherit from collections Mapping explicitly just in case   In Python 3  there are a number of improvements to be made  As of Python 3 3  abstract base classes live in collections abc  They remain in collections too for backwards compatibility  but it s nicer having our abstract base classes together in one namespace  So this imports abc from collections  Python 3 3 also adds yield from  which is designed for just these sorts of situations  This is not empty syntactic sugar  it may lead to faster code and more sensible interactions with coroutines   from collections import abc def nested dict iter nested       for key  value in nested items            if isinstance value  abc Mapping               yield from nested dict iter value          else              yield key  value

User · Answer

Here s a modified version of Fred Foo s answer for Python 2  In the original response  only the deepest level of nesting is output  If you output the keys as lists  you can keep the keys for all levels  although to reference them you need to reference a list of lists    Here s the function    def NestIter nested       for key  value in nested iteritems            if isinstance value  collections Mapping               for inner key  inner value in NestIter value                   yield  key  inner key   inner value         else              yield  key  value   To reference the keys    for keys  vals in mynested       print mynested keys 0   keys 1  0   keys 1  1  0      for a three-level dictionary    You need to know the number of levels before to access multiple keys and the number of levels should be constant  it may be possible to add a small bit of script to check the number of nesting levels when iterating through values  but I haven t yet looked at this

User · Answer

Slightly different version I wrote that keeps track of the keys along the way to get there  def print dict v  prefix          if isinstance v  dict           for k  v2 in v items                p2              format prefix  k              print dict v2  p2      elif isinstance v  list           for i  v2 in enumerate v               p2            format prefix  i              print dict v2  p2      else          print           format prefix  repr v      On your data  it ll print  data  xml    config    portstatus    status     u good  data  xml    config    target     u 1  data  xml    port     u 11    It s also easy to modify it to track the prefix as a tuple of keys rather than a string if you need it that way

User · Answer

I find this approach a bit more flexible  here you just providing generator function that emits key  value pairs and can be easily extended to also iterate over lists   def traverse value  key None       if isinstance value  dict           for k  v in value items                yield from traverse v  k      else          yield key  value   Then you can write your own myprint function  then would print those key value pairs   def myprint d       for k  v in traverse d           print f  k     v      A test   myprint        xml              config                  portstatus                      status    good                               target    1                       port    11               Output   status   good target   1 port   11   I tested this on Python 3 6

User · Answer

A alternative solution to work with lists based on Scharron s solution  def myprint d       my list   d iteritems   if isinstance d  dict  else enumerate d       for k  v in my list          if isinstance v  dict  or isinstance v  list               myprint v          else              print u  0     1   format k  v

User · Answer

Alternative iterative solution   def myprint d       stack   d items       while stack          k  v   stack pop           if isinstance v  dict               stack extend v iteritems            else              print   s   s     k  v

User · Answer

There are potential problems if you write your own recursive implementation or the iterative equivalent with stack  See this example      dic          dic  quot key1 quot            dic  quot key1 quot    quot key1 1 quot      quot value1 quot      dic  quot key2 quot             dic  quot key2 quot    quot key2 1 quot      quot value2 quot      dic  quot key2 quot    quot key2 2 quot     dic  quot key1 quot       dic  quot key2 quot    quot key2 3 quot     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 lt -------back edge                                                                    key1     key2                                                                       - gt 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  quot  0     1  quot  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  quot  s   s quot     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      quot       quot  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  quot  s   s quot     k  v            visited add k

User · Answer

Iterative solution as an alternative   def traverse nested dict d       iters    d iteritems         while iters          it   iters pop           try              k  v   it next           except StopIteration              continue          iters append it           if isinstance v  dict               iters append v iteritems            else              yield k  v   d     a   1   b   2   c     d   3   e     f   4    for k  v in traverse nested dict d       print k  v

[python] Loop through all nested dictionary values?

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