Joao S. O. Bueno wrote:
> However, as noted, there is no way to customize Python JSON encoder
> to encode an arbitrary decimal number in JSON, even though the standard does
> allow it, and Python supports then via decimal.Decimal.
> Short of a long term solution, like a __json__ protocol, or at least special
> support in Python json module for objects of type "numbers.Number",
> the only way to go, is, as you are asking, being able to insert "raw
> strings into json".
Would the approach I outlined in my answer to Dominik be acceptable?:
1) Add keyword argument to `json.dump(s)` called `dump_float` which will act as
a counter part to `parse_float` keyword argument in `json.load(s)`. The
argument will accept custom type (class) for the user's "float" representation
(for example `decimal.Decimal`).
2) If specified by the client code, JSONEncoder, when identifying object of
that type in the input data will encode it using the special rule suggested by
Dominik:
```
# if o is custom float type
if isinstance(o, <dump_float Type>):
dump_val = str(o)
try:
float(dump_val)
except ValueError:
raise TypeError('... is not JSON serializable float number') from None
<write dump_val to the stream>
```
This would have following implications/consequences:
1) str(o) may return invalid float, but the check will not let it into the
stream.
2) the contract between the custom float class implementation and standard
`json` module will be pretty clear - it must implement the serialization in its
__str__ function and must return valid float.
3) the standard implementation does not need to `import decimal`. If the client
code needs this feature, it will `import decimal` itself.
4) definition which class/type objects should be handled by this rule will be
pretty clear, it will be the only one specified in `dump_float` argument (if
specified at all).
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