Chaining kwargs in a function call

Question

I have an AND and OR function that evaluates an expression. I would like to chain these items together into something like this:

>>> AND(
        # kwarg
        Neutered=True, 
        # reduces/evaluates to arg/value
        OR(Black=False, AND(Female=False, NOT(White=True)), AND(NOT(Female=False), OR(White=True, Tan=True))))

However, I get this error when doing so:

SyntaxError: positional argument follows keyword argument

This is because the OR evaluates to a boolean and not a kwarg, which is how it needs to be passed. What would be a good way to get around this issue?

@MarkMeyer there can also be multiple levels of nesting and I'm not quite sure which part will evaluate to a value (such as "OR(...)" and which is just a variable). — David542, Mar 22 '20 at 19:49
@DeepSpace one option I thought was to wrap all the kwargs in something like a new class that defers evaluation, such as `Var(...)` -- but I'm looking for perhaps someone with a much better understanding of python to offer some solutions. — David542, Mar 22 '20 at 19:50

score 1 · Accepted Answer · answered Mar 22 '20 at 20:06

1

Simply rearrange the call to have the kwargs after the args:

AND(
    OR(AND(NOT(White=True), Female=False), AND(NOT(Female=False), OR(White=True, Tan=True)), Black=False),
    Neutered=True)

Or, if possible, use the dict unpacking operator:

AND(
    Neutered=True,
    **OR(Black=False, **AND(Female=False, **NOT(White=True)), **AND(NOT(Female=False), OR(White=True, Tan=True))))

answered Mar 22 '20 at 20:06

wjandrea

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I like both approaches. The first one works when testing it, for the second one I get `TypeError: type object argument after ** must be a mapping, not NOT` -- it might be how tightly `**` binds but not entirely sure. – David542 Mar 22 '20 at 20:09
to simplify it, doing `AND(Neutered=True, **OR(Black=False, Blue=False))` gives me the same. – David542 Mar 22 '20 at 20:11
1

@David542 That means your classes aren't mappings (like a dict), which I guess means the second option isn't possible. If they should be mappings, check out [How to correctly implement the mapping protocol in Python?](https://stackoverflow.com/q/19775685/4518341) – wjandrea Mar 22 '20 at 20:12

Chaining kwargs in a function call

1 Answers1