Use pprint

import pprint

x  = {
  'planet' : {
    'name' : 'Earth',
    'has' : {
      'plants' : 'yes',
      'animals' : 'yes',
      'cryptonite' : 'no'
    }
  }
}
pp = pprint.PrettyPrinter(indent=4)
pp.pprint(x)

This outputs

{   'planet': {   'has': {   'animals': 'yes',
                             'cryptonite': 'no',
                             'plants': 'yes'},
                  'name': 'Earth'}}

Play around with pprint formatting and you can get the desired result.

• http://docs.python.org/library/pprint.html

Using built-in vim features:

In a terminal: pip install autopep8
Then, in vim: au FileType python setlocal formatprg=autopep8\ -, then select your dictionary and gq.

Using a plugin: check out https://github.com/Chiel92/vim-autoformat. That's one of many plugins that can automatically format code for you.

I'm not sure how exactly you want the formatting to look like, but you could start with a function like this:

def pretty(d, indent=0):
   for key, value in d.items():
      print('\t' * indent + str(key))
      if isinstance(value, dict):
         pretty(value, indent+1)
      else:
         print('\t' * (indent+1) + str(value))