Python format error

error.txt

body = ('''
{ 
  "beacons": [
    { 
      "url" : "http://127.0.0.1:{0}",
      "action": "return_204"
    }
  ],
  "version": "0.1"
}
'''
).format(666)

Error:

Running Test beacon_intercept:
Generating Report: --------------
 Test: beacon_intercept: Exception
    File: beacon_intercept.test.py
    Directory: /Users/wkaras/REPOS/YTS/tests/gold_tests/pluginTest/beacon_intercept
     Reason: Traceback (most recent call last):
       File "/Users/wkaras/REPOS/YTS/tests/env-test/lib/python3.5/site-packages/autest/core/runtesttask.py", line 34, in __call__
         tl = self.__logic.Run(self.__test)
       File "/Users/wkaras/REPOS/YTS/tests/env-test/lib/python3.5/site-packages/autest/runlogic/runlogic.py", line 18, in Run
         if not tmp.Start(obj):
       File "/Users/wkaras/REPOS/YTS/tests/env-test/lib/python3.5/site-packages/autest/runlogic/test.py", line 89, in Start
         loadTest(self.__test)
       File "/Users/wkaras/REPOS/YTS/tests/env-test/lib/python3.5/site-packages/autest/core/test.py", line 179, in loadTest
         execFile(fileName, locals, locals)
       File "/Users/wkaras/REPOS/YTS/tests/env-test/lib/python3.5/site-packages/autest/common/execfile.py", line 15, in execFile
         exec (safeCompile(f.read(), fname), globals, locals)
       File "/Users/wkaras/REPOS/YTS/tests/gold_tests/pluginTest/beacon_intercept/beacon_intercept.test.py", line 50, in <module>
         ).format(666)
     KeyError: '\n  "beacons"'