Arkadir on Reasons to use protocol buffers instead of JSON

Comment on Reasons to use protocol buffers instead of JSON parent

structure = json.loads(json_string)

Not quite. Let's say your JSON data contains the following attribute:

    "access" : [ "view", "edit", "admin" ],

This field should be represented (in the language) as a set of values from an "access-levels" enumeration.

In C#, you'd have the following boilerplate:

    [DataMember(Name = "access")]
    public HashSet<AccessLevels> Access { get; private set; }

In OCaml, it would be:

    access : Access.Set.t ;

The simple "json.loads" solution would return a list of strings instead. What's the Python code for turning it into a set of enumeration values, and failing if one of the values does not match ?

falcolas 12y

Python doesn't have enumerations, per se. Here's how I'd represent that:

    if 'edit' in structure['access']:
         # can edit

In which case it really doesn't matter if there's junk in access. If I really felt the need to validate the structure, I could do so with:

    if not set(structure['access']).issubset(all_access_privs):
        raise ValueError('invalid access types passed in')

but more realistically, I'd rely on the ORM object to validate against the authoritative source - the database - and key off the errors there.

TomaszZielinski 12y

Python 3.4 has enums, if that's what you meant: https://docs.python.org/3/library/enum.html

colanderman 12y

But that's not a problem with JSON-the-serialization; that just means JSON begs to be extended with a rich schema definition language.

It's kind of like saying "language X sucks because it doesn't have an automatic build tool; use language Y instead". You just need a build tool for X, not a new language.

PaulFreund 12y

http://json-schema.org/

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