Why does Python json module represent floats in dictionary keys as strings?

Question

See the following code:

>>> import json
>>> m = {}
>>> m[0.0] = 1.0
>>> json.dumps(m)
'{"0.0": 1.0}'

In the value of the JSON, we have 1.0. But in the key we have "0.0" (a Json string).

This ambiguous handling of floats just cost me some debugging time. Does anyone know why python's json module does this?

Thanatos · Accepted Answer · 2011-04-03 01:37:58Z

9

Because a JSON key must be a string. See the RFC.

answered Apr 3, 2011 at 1:37

Thanatos

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2 Comments

Winston Ewert Over a year ago

It's worth noting that despite popular opinion, JSON is precisely defined subset of Javascript, not just anything that's valid javascript literals. Although this case, IMO, should probably have thrown an exception.

Max Over a year ago

Agreed, should have thrown an exception in this case, it would've been clearer to me from the outset. Python's cjson module does this.

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