pip install httmock

emerge dev-python/httmock

from httmock import urlmatch, HTTMock
import requests

@urlmatch(netloc=r'(.*\.)?google\.com$')
def google_mock(url, request):
    return 'Feeling lucky, punk?'

with HTTMock(google_mock):
    r = requests.get('http://google.com/')
print r.content  # 'Feeling lucky, punk?'

from httmock import all_requests, HTTMock
import requests

@all_requests
def response_content(url, request):
	return {'status_code': 200,
	        'content': 'Oh hai'}

with HTTMock(response_content):
	r = requests.get('https://foo_bar')

print r.status_code
print r.content

from httmock import all_requests, response, HTTMock
import requests

@all_requests
def response_content(url, request):
	headers = {'content-type': 'application/json',
	           'Set-Cookie': 'foo=bar;'}
	content = {'message': 'API rate limit exceeded'}
	return response(403, content, headers, None, 5, request)

with HTTMock(response_content):
	r = requests.get('https://api.github.com/users/whatever')

print r.json().get('message')
print r.cookies['foo']