[New-bugs-announce] [issue24641] Log type of unserializable value when raising JSON TypeError

[Madison May]

New submission from Madison May:

Currently the json lib only logs the string representation of the variable, which does not always include type information.

I recently ran into a difficult to debug issue with code similar to the following:

```
import json
import numpy as np
d = {'data': np.int16(5)}
json.dumps(d)
```

which produces the following error:

```
TypeError: 5 is not JSON serializable
```

It took us quite a while to determine that `5` was actually of type `np.int` instead of the native type.

A cursory glance at StackOverflow suggests that I'm not alone in running into this issue: http://stackoverflow.com/questions/10872604/json-dump-throwing-typeerror-is-not-json-serializable-on-seemingly-vali


I'd like to consider modifying the error message to be more similar to the following:

```
TypeError: 5 of type `numpy.int16` is not JSON serializable
```

----------
components: Library (Lib)
messages: 246776
nosy: Madison May
priority: normal
severity: normal
status: open
title: Log type of unserializable value when raising JSON TypeError
versions: Python 2.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24641>
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