title: Get a list of all keys in nested dictionary
body: <p>I want to get a list of all keys in a nested dictionary that contains lists and dictionaries.</p>
  
  <p>I currently have this code, but it seems to be missing adding some keys to the list and also duplicate adds some keys.</p>
  
  <pre><code>keys_list = []
  def get_keys(d_or_l, keys_list):
      if isinstance(d_or_l, dict):
          for k, v in iter(sorted(d_or_l.iteritems())):
              if isinstance(v, list):
                  get_keys(v, keys_list)
              elif isinstance(v, dict):
                  get_keys(v, keys_list)
              else:
                  keys_list.append(k)
      elif isinstance(d_or_l, list):
          for i in d_or_l:
              if isinstance(i, list):
                  get_keys(i, keys_list)
              elif isinstance(i, dict):
                  get_keys(i, keys_list)
      else:
          print "** Skipping item of type: {}".format(type(d_or_l))
      return keys_list
  </code></pre>
  
  <p>This just takes an empty list and populates it with the keys. d_or_l is a variable and takes the original dict to compare it against.</p>