[issue34972] json dump silently converts int keys to string

[My-Tien Nguyen]

Change by My-Tien Nguyen :


--
nosy: My-Tien Nguyen
priority: normal
severity: normal
status: open
title: json dump silently converts int keys to string

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[issue34972] json dump silently converts int keys to string

[My-Tien Nguyen]

New submission from My-Tien Nguyen :

When int keys are silently converted to string on json serialization, the user 
needs to remember to convert it back to int on loading.
I think that a warning should be shown at least.

In my case I serialize a dict to json with int keys, later load it back into a 
dict (resulting in a dict with string keys) and test for existence of an int 
key in the dict which will then return False incorrectly.

I am aware that json does not support int keys, but this can be easily 
forgotten.

--
components: +Library (Lib)
type:  -> behavior
versions: +Python 3.6

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[issue34972] json dump silently converts int keys to string

[My-Tien Nguyen]

My-Tien Nguyen  added the comment:

I don’t think, “other languages do that too” is a good argument here. This 
would apply if behaving differently would break user expectation. But here we 
would do nothing more than explicitly inform the user of a relevant operation. 
If they already expected that behaviour, they can disregard the warning.

I don’t see how `parse_int`would help me here, I would need a `parse_str=int`, 
but then it would try to parse every string, and I don’t see the use case for 
that.

I would suggest a warning similar to this:

--- json/encoder.py
+++ json/encoder.py
@@ -1,6 +1,7 @@
 """Implementation of JSONEncoder
 """
 import re
+import warnings
 
 try:
 from _json import encode_basestring_ascii as c_encode_basestring_ascii
@@ -353,7 +354,9 @@
 items = sorted(dct.items(), key=lambda kv: kv[0])
 else:
 items = dct.items()
+non_str_key = False
 for key, value in items:
+non_str_key = non_str_key or not isinstance(key, str)
 if isinstance(key, str):
 pass
 # JavaScript is weakly typed for these, so it makes sense to
@@ -403,6 +406,8 @@
 else:
 chunks = _iterencode(value, _current_indent_level)
 yield from chunks
+if non_str_key:
+warnings.warn("Encountered non-string key(s), converted to 
string.", RuntimeWarning)
 if newline_indent is not None:
 _current_indent_level -= 1
 yield '\n' + _indent * _current_indent_level

--

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[issue34972] json dump silently converts int keys to string

[My-Tien Nguyen]

My-Tien Nguyen  added the comment:

Sure, I can do that, but wanted to propose this regardless. I guess this is a 
disagreement on a language design level.
As a proponent of strong typing I wouldn’t have allowed non-string keys in the 
first place, and if they are allowed I would warn about conversion. This is 
also more aligned with the “explicit is better than implicit” principle.

--
resolution: not a bug -> 
status: closed -> open

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[issue34972] json dump silently converts int keys to string

[My-Tien Nguyen]

Change by My-Tien Nguyen :


--
status: open -> closed

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