JSON conversion to single quotes
No, that code is not enough to handle any valid JSON.

Here are two examples where the result is not only different from the expected, but also unparsable:

The string:

{"hello":"wor\":ld"}


will be converted to:

{'hello':'wor':ld'}


The string:

{"hello":"w''orld"}


will be converted to:

{'hello':'w\''orld'}