String format a json String gives KeyError
Why does this code give a KeyError?
output_format = '{ "File": "{filename}", "Success": {success}, "ErrorMessage": "{error_msg}", "LogIdentifier": "{log_identifier}" }' print output_format.format(filename='My_file_name', success=True, error_msg='', log_identifier='123')
Error message
KeyError: ' "File"'
Answers
You need to double the outer braces; otherwise Python thinks { "File".. is a reference too:
output_format = '{{ "File": "{filename}", "Success": {success}, "ErrorMessage": "{error_msg}", "LogIdentifier": "{log_identifier}" }}'
Result:
>>> print output_format.format(filename='My_file_name', ... success=True, ... error_msg='', ... log_identifier='123') { "File": "My_file_name", "Success": True, "ErrorMessage": "", "LogIdentifier": "123" }
If, indicentally, you are producing JSON output, you'd be better off using the json module:
>>> import json >>> print json.dumps(dict(File='My_file_name', ... Success=True, ... ErrorMessage='', ... LogIdentifier='123')) {"LogIdentifier": "123", "ErrorMessage": "", "Success": true, "File": "My_file_name"}
Note the lowercase true in the output, as required by the JSON standard.