Storing lambdas in a dictionary

Question

I have been trying to create a dictionary with a string for each key and a lambda function for each value. I am not sure where I am going wrong but I suspect it is either my attempt to store a lambda in a dictionary in the first place, or the fact that my lambda is using a shortcut operator.

Code:

dict = {
    'Applied_poison_rating_bonus': 
        (lambda target, magnitude: target.equipmentPoisonRatingBonus += magnitude)
}

The error being raised is SyntaxError: invalid syntax and pointing right at my +=. Are shortcut operators not allowed in lambdas, or am I even farther off track than I thought?

For the sake of sanity, I have omitted hundreds of very similar pairs (It isn’t just a tiny dictionary.)

EDIT:

It seems my issue was with trying to assign anything within a lambda expression. Howver, my issue to solve is thus how can I get a method that only knows the key to this dictionary to be able to alter that field defined in my (broken) code?

Would some manner of call to eval() help?

EDIT_FINAL:

The functools.partial() method was recommended to this extended part of the question, and I believe after researching it, I will find it sufficient to solve my problem.

Asked By: BlackVegetable

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Source

Answer 1

You cannot use assignments in a expression, and a lambda only takes an expression.

You can store lambdas in dictionaries just fine otherwise:

dict = {'Applied_poison_rating_bonus' : (lambda target, magnitude: target.equipmentPoisonRatingBonus + magnitude)}

The above lambda of course only returns the result, it won’t alter target.equimentPoisonRatingBonus in-place.

Answered By: Martijn Pieters

Storing lambdas in a dictionary

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