pyDatalog / pyDatalog /

The default branch has multiple heads


Copyright (C) 2012 Pierre Carbonnelle

This library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc.  51 Franklin St, Fifth Floor, Boston, MA 02110-1301

This work is derived from Pythologic, (C) 2004 Shai Berger, 
in accordance with the Python Software Foundation licence.
(See and )

methods / classes exposed by this file:
methods for direct access to datalog knowledge base:
  * assert_fact(predicate_name, *args) : assert predicate_name(args)
  * retract_fact(predicate_name, *args) : retracts predicate_name(args)
  * program() : decorator function to create datalog programs
  * predicate() : decorator function to create a predicate resolver in python
  * load(code) : loads the clauses contained in the code string
  * ask(code) : returns the result of the query contained in the code string
  * variables(n) : convenience function to create multiple variables in one statement
  * clear() : resets the datalog database
DatalogError class
Answer class defines the object returned by ask()
  * __eq__ for equality test
  * __str__ for printing
classes for Python Mixin:
  * Variable : a class to define Variable, for use in datalog queries
  * Mixin : a class that can be mixed in another class to give it datalog capability
  * sqlMetaMixin : a metaclass to be used when creating a class with both SQLAlchemy and datalog capability
from collections import defaultdict
import inspect
import six
import string
import sys
import weakref

    from . import version
    from . import pyEngine
    from . import pyParser
    from .pyParser import Symbol, Expression, Lambda, Literal, Body
except ValueError:
    import version
    import pyEngine
    import pyParser
    from pyParser import Symbol, Expression, Lambda, Literal, Body
print("pyDatalog version %s" % version.__version__)

    from sqlalchemy.ext.declarative import DeclarativeMeta
    DeclarativeMeta = object

class Dummy(object):
    from sqlalchemy.orm.attributes import InstrumentedAttribute
    InstrumentedAttribute = Dummy # not used; could be any class, really

""" ****************** direct access to datalog knowledge base ***************** """
class DatalogError(Exception):
    def __init__(self, value, lineno, function):
        self.value = value
        self.lineno = lineno
        self.function = function
    def __str__(self):
        return "%s\nin line %s of %s" % (self.value, self.lineno, self.function)        

def assert_fact(predicate_name, *args):
    """ assert predicate_name(args) """
    literal = Literal.make(predicate_name, args)

def retract_fact(predicate_name, *args):
    """ retracts predicate_name(args) """
    literal = Literal.make(predicate_name, args)

def program():
    """ A decorator for datalog program  """
    return pyParser.add_program

def predicate():
    """decorator function to create a predicate resolver in python"""
    return _predicate 

def _predicate(func):
    arity = len(inspect.getargspec(func)[0])
    pyEngine.Python_resolvers[func.__name__ + '/' + str(arity)] = func
    return func

def load(code):
    """loads the clauses contained in the code string """
    return pyParser.load(code)

def ask(code, _fast=None):
    """returns the result of the query contained in the code string"""
    return pyParser.ask(code, _fast)

def clear():
    """ resets the default datalog database """

class Answer(object):
    """ object returned by ask() """
    def __init__(self, name, arity, answers): = name
        self.arity = arity
        self.answers = answers

    def __eq__ (self, other):
        return set(self.answers) == other if self.answers else other is None
    def __str__(self):
        return str(set(self.answers))

def create_atoms(*args):
    stack = inspect.stack()
        locals_ = stack[1][0].f_locals
        for arg in set(args + ('_sum','_min', '_max', '_len')):
            if arg in locals_: 
                assert isinstance(locals_[arg], (pyParser.Symbol, pyDatalog.Variable)), \
                    "Name conflict.  Can't redefine %s as atom" % arg
                if arg[0] not in string.ascii_uppercase:
                    locals_[arg] = pyParser.Symbol(arg)
                    locals_[arg] = pyDatalog.Variable()    
        del stack

def variables(n):
    return [pyDatalog.Variable() for i in range(n)]

#utility functions, also used by pyParser

def _assert_fact(literal):
    clause = pyEngine.Clause(literal.lua, [])
def _retract_fact(literal):
    clause = pyEngine.Clause(literal.lua, [])

def add_clause(head,body):
    if isinstance(body, Body):
        tbl = [a.lua for a in body.literals]
    else: # body is a literal
        tbl = (body.lua,)
    clause = pyEngine.Clause(head.lua, tbl)
    return pyEngine.assert_(clause)

#circ: share functions with pyParser and avoid circular import
pyDatalog = Dummy()
pyDatalog.DatalogError= DatalogError
pyDatalog.add_clause = add_clause
pyDatalog._assert_fact = _assert_fact
pyDatalog._retract_fact = _retract_fact
pyDatalog.Answer = Answer
pyParser.pyDatalog = pyDatalog
pyEngine.pyDatalog = pyDatalog

""" ****************** python Mixin ***************** """

class Variable(pyParser.VarSymbol, pyParser.LazyList):
    def __init__(self):
        pyParser.VarSymbol.__init__(self, 'X%i' % id(self))
pyDatalog.Variable = Variable

"""Keep a dictionary of classes with datalog capabilities.  This list is used by pyEngine to resolve prefixed literals."""
Class_dict = {}
pyEngine.Class_dict = Class_dict # TODO better way to share it with ?

class metaMixin(type):
    """Metaclass used to define the behavior of a subclass of Mixin"""
    __refs__ = defaultdict(weakref.WeakSet)
    def __init__(cls, name, bases, dct):
        """when creating a subclass of Mixin, save the subclass in Class_dict. """
        super(metaMixin, cls).__init__(name, bases, dct)
        cls.has_SQLAlchemy = any(base.__module__ in ('sqlalchemy.ext.declarative',) for base in bases)
        def _getattr(self, attribute):
            """ responds to instance.method by asking datalog engine """
            if not attribute == '__iter__' and not attribute.startswith('_sa_'):
                predicate_name = "%s.%s[1]==" % (self.__class__.__name__, attribute)
                literal = Literal.make(predicate_name, (self, Symbol("X")))
                result = literal.lua.ask(False)
                return result[0][-1] if result else None                    
            raise AttributeError
        cls.__getattr__ = _getattr   
    def __getattr__(cls, method):
        """when access to an attribute of a subclass of Mixin fails, return an object that responds to () and to [] """
        if cls in ('Mixin', 'metaMixin') or method in (
                '__mapper_cls__', '_decl_class_registry', '__sa_instrumentation_manager__', 
                '__table_cls__', '_pyD_query'):
            raise AttributeError
        return pyParser.Symbol("%s.%s" % (cls.__name__, method))

    def pyDatalog_search(cls, literal):
        """Called by pyEngine to resolve a prefixed literal for a subclass of Mixin."""
        terms = literal.terms
        attr_name = literal.pred.suffix
        operator = (']')[1:2]+[None])[0] # what's after ']' or None
        # TODO check prearity
        def check_attribute(X):
            if attr_name not in X.__dict__ and attr_name not in cls.__dict__:
                raise AttributeError("%s does not have %s attribute" % (cls.__name__, attr_name))

        if len(terms)==2:
            X, Y = terms[0], terms[1]
            if X.is_const():
                # try accessing the attribute of the first term in literal
                Y1 = getattr(, attr_name)
                if not Y.is_const() or not operator or,operator,
                    yield (, if Y.is_const() else Y1 if operator=='==' else None)
            elif cls.has_SQLAlchemy:
                if cls.session:
                    q = cls.session.query(cls)
                    if Y.is_const():
                        q = q.filter(, attr_name), operator,
                    for r in q:
                        Y1 = getattr(r, attr_name)
                        if not Y.is_const() or not operator or,operator,
                                yield (r, if Y.is_const() else Y1 if operator=='==' else None)
                # python object with Mixin
                for X in metaMixin.__refs__[cls]:
                    Y1 = getattr(X, attr_name)
                    if not Y.is_const() or not operator or,operator,
                        yield (X, if Y.is_const() else Y1 if operator=='==' else None)
            raise AttributeError ("%s could not be resolved" %

# following syntax to declare Mixin is used for compatibility with python 2 and 3
Mixin = metaMixin('Mixin', (object,), {})
pyDatalog.Mixin = Mixin

""" When creating a Mixin object without SQLAlchemy, add it to the list of instances,
    so that it can be included in the result of queries"""
def __init__(self):
    if not self.__class__.has_SQLAlchemy:
        for cls in self.__class__.__mro__:
            if cls.__name__ in Class_dict and cls not in (pyDatalog.Mixin, object):
Mixin.__init__ = __init__

""" ****************** support for SQLAlchemy ***************** """

class sqlMetaMixin(metaMixin, DeclarativeMeta): 
    """ metaclass to be used with Mixin for SQLAlchemy"""

""" attach a method to SQLAlchemy class.attribute, 
    so that it can answer queries like class.attribute[X]==Y"""
def InstrumentedAttribute_getitem(self, *args):
    cls = self.class_
    method = self.key
    return type(cls).__getattr__(cls, method).__getitem__(*args)
InstrumentedAttribute.__getitem__ = InstrumentedAttribute_getitem