Not iterable object in python

Question

I am trying to write a function that returns the variables contained in a class of type Rule. I need to iterate through it and get all variables and store them in a set.

class Rule:
    # head is a function
    # body is a *list* of functions
    def __init__(self, head, body):
        self.head = head
        self.body = body
    def __str__(self):
        return str(self.head) + ' :- ' + str(self.body)
    def __eq__(self, other):
        if not isinstance(other, Rule):
            return NotImplemented
        return self.head == other.head and self.body == other.body
    def __hash__(self):
        return hash(self.head) + hash(self.body)


class RuleBody:
    def __init__(self, terms):
        assert isinstance(terms, list)
        self.terms = terms
    def separator(self):
        return ','
    def __str__(self):
        return '(' + (self.separator() + ' ').join(
            list(map(str, self.terms))) + ')'
    def __eq__(self, other):
        if not isinstance(other, RuleBody):
            return NotImplemented
        return self.terms == other.terms
    def __hash__(self):
        return hash(self.terms)

My function is the following:

def variables_of_clause (self, c : Rule) -> set :
        returnSet = set()
        l = getattr(c, 'body')
        for o in l:
            returnSet.add(o)

Testing function

# The variables in a Prolog rule p (X, Y, a) :- q (a, b, a) is [X; Y]
def test_variables_of_clause (self):
        c = Rule (Function ("p", [Variable("X"), Variable("Y"), Atom("a")]),
                    RuleBody ([Function ("q", [Atom("a"), Atom("b"), Atom("a")])]))
        #assert
        (self.variables_of_clause(c) == set([Variable("X"), Variable("Y")]))

I keep getting an error that says: TypeError: 'RuleBody' is not iterable.

Seems like the thing you want to iterate through is the terms of your RuleBody, e.g. l.terms — khelwood
– khelwood, Commented May 10, 2020 at 21:25
What part of my code do I change to l.terms? It does not work if I change my for loop to it. — hussain sagar
– hussain sagar, Commented May 10, 2020 at 22:24
If the error emanates from for o in l: and l is an instance of RuleBody then you could try for o in l.terms: — khelwood
– khelwood, Commented May 10, 2020 at 22:30
I did that. Now I get errors from the last function in RuleBody which says " TypeError: unhashable type: 'list' " — hussain sagar
– hussain sagar, Commented May 10, 2020 at 22:35
So one error is solved and you now have another one to figure out. Perhaps you would like to post a question with a minimal reproducible example and a traceback of the exception this time. — khelwood
– khelwood, Commented May 10, 2020 at 22:36

Djaouad · Accepted Answer · 2020-05-10 21:33:04Z

2

RuleBody.terms is a list, not RuleBody, you can iterate over RuleBody.terms instead, however, you can make your RuleBody class iterable (by basically making it return RuleBody.terms's elements), using the __iter__ method:

class RuleBody:
    ... # everything
    ...
    def __iter__(self):
        return iter(self.terms)

edited May 10, 2020 at 21:33

answered May 10, 2020 at 21:27

Djaouad

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2 Comments

Djaouad Over a year ago

@PatrickArtner I was just so used to using dunders inside class definitions, I realize using the built-in is better. Thx.

hussain sagar Over a year ago

Thank you for your answer. Unfortunately, I cannot change my class. I can only change the code in my function.

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