Why does `curl` post request work fine but not the `python_client` request?

curl.txt

curl -i -H "Content-Type: application/json" -X POST -d '{"url_id":"1", "results":{"pinterest":{"pin_count":"3"}, "facebook":{"comment_count":"101","like_count":"44","share_count":"99"}, "twitter":{"share_count":"77"}, "google":{"plus_count":"5"}}}' http://localhost:5000/api/v1/store_results

python_client.py

import requests

BASE_URL = "http://localhost:5000/api/v1/"

post_obj = {'results': {'facebook': {u'comment_count': 247,
  'like_count': 406,
  'share_count': 425},
  'google': {'plus_count': 18},
  'pinterest': {'pin_count': 3758},
  'twitter': {'share_count': 21}},
  'url_id': 1}
 
headers = {'Content-type': 'application/json'}

# POST results to API
p = requests.post(BASE_URL + 'store_results', data=json.dumps(post_obj))
print p
# 500