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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def evaluate_formula(formula, variables):
 """Very simple formula evaluator. Beware the security. :param formula: A simple formula. :type formula: str :param variables: A collection of variable (key and value). :type variables: dict :returns: The result of the formula execution. :rtype: float, int """

    for key, value in list(variables.items()):
        if value is None or (hasattr(value, 'isNull') and value.isNull()):
            # If one value is null, we return null.
            return value
        formula = formula.replace(key, str(value))
    result = eval(formula)
    return result