json cannot serialize circular references

[dbieber]

Here's a minimal example of the failure:

import fire
x = {}
x['y'] = x
fire.Fire()

Running python example.py gives this traceback:

Traceback (most recent call last):
  File "example.py", line 4, in <module>
    fire.Fire()
  File "/Users/dbieber/virtualenvs/_/lib/python2.7/site-packages/fire/core.py", line 145, in Fire
    _PrintResult(component_trace, verbose=component_trace.verbose)
  File "/Users/dbieber/virtualenvs/_/lib/python2.7/site-packages/fire/core.py", line 181, in _PrintResult
    print(_DictAsString(result, verbose))
  File "/Users/dbieber/virtualenvs/_/lib/python2.7/site-packages/fire/core.py", line 210, in _DictAsString
    key=str(key) + ':', value=_OneLineResult(value))
  File "/Users/dbieber/virtualenvs/_/lib/python2.7/site-packages/fire/core.py", line 230, in _OneLineResult
    return json.dumps(result)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 243, in dumps
    return _default_encoder.encode(obj)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 207, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 270, in iterencode
    return _iterencode(o, 0)
ValueError: Circular reference detected

The problem is that _DictAsString tries to serialize [each key of] the dict using json, but json cannot serialize dicts w/ circular references.

We'll need a different serialization technique to support this case.

[dbieber]

Saurabh may take this as a first task.

[saurabhkpatel]

I will submit the pull request soon for this bug.
My thoughts are something like this:

Handle extra type of exception and add the appropriate message in front of the particular key. In the below example, key's value is represented same like this.

fire: <module 'fire' from '/Users/srpatel/github/python-fire/fire/__init__.pyc'>
x:    {'y': {...}}

[dbieber]

Fixed by #49, thank you Saurabh!