Hacker News Reader

Hacker News

Comment by cyberlis | Hacker News Reader

Full thread

cyberlis

Recently I was interested in parsing. Real parsing with grammars BNF LL LR.. :)

As exercise I implemented a library to query dicts.

This is my first python library and I'm looking for feedback and criticism

Especially, I need advice about public API

https://github.com/cyberlis/dictquery

You can install it with:

pip install dictquery

To write it I read:

Python Cookbook third edition. 2.18 Tokenizing Text, 2.19 Writing a Simple Recursive Descent Parser

All parsing related articles from https://eli.thegreenplace.net/2010/01/02/top-down-operator-p...

https://docs.python.org/3/library/re.html#writing-a-tokenize...

View on HN

I really don't like the stringly API.

It'll defeat anything my editor can predict, making typos easier. It also makes it harder to reason about types, as I have to trust the library to make the right assumption. [0]

Instead of:

    dq.match(data, "`friends.age` <= 26")

Why not:

    import operator # from the standard library

    dq.match(data, "friends.age", operator.le, 26)

It'll simplify your parsing, works with my editor, and makes it easier to reason about types. You'll still need to parse, as you're basically handling a variadic function, but the user can hand you an AST.

---

[0] For example, what type would occur if:

    dq.match(data, "`friends.age` <= 26.")

Does 26 become a float? Or an integer? Or raise a ParseError?

I have to consider that with a string, less so with Python's own objects.

if you need a nested key value, you can use function:

    def get_dict_value(query_dict, dict_key, use_nested_keys=True,
                       key_separator='.', raise_keyerror=False):

theoretically i can make alternative syntax.

The plus of "stringly API" is that you can save your queries in database, or get it through web interface

> The plus of "stringly API" is that you can save your queries in database, or get it through web interface

You can do the same with a function call, there's no difference, apart from already having a list of arguments to pass around. (And of course, the type uncertainty you get with a value stored in a string.)

> if you need a nested key value, you can use function:

Not sure why you're telling me that. What part of my comment are you responding to?

Actually why not overload operators to do something like:

dq.match(data, Field("friends.age") <= 26)

or in the appengine style if data is some class (say Friend):

dq.match(data, Friend__age <= 26)

Reply on news.ycombinator.com