pyDatalog adds the logic Programming paradigm to Python's toolbox, in a pythonic way.

1. Logic Programming in Python
Pierre Carbonnelle
FOSDEM 2014

2. No if’s, no loops, just the plain mathematical definition !

3. Logic programming
(Prolog, SQL)
Functional
(Lisp, ..)
Imperative / OO
(C, Smalltalk)

4. Logic programming
(Prolog, SQL)
Functional
(Lisp, ..)
Imperative / OO
(C, Smalltalk)
Python
Python + pyDatalog

5. Why Logic Programming in Python ?
Be productive
Be Readable
Use AI
Easy to learn
Batteries included
Query 11 SQL databases

6. The anatomy of a prolog program
Fact
Clause
Query

7. The anatomy of a pyDatalog program

8. The anatomy of a pyDatalog program

9. Sample 1
Could be
written in SQL
too !

10. Sample 1
 Loop
 Calculation
 Test
 Input/output polymorphism !
Shorter
programs !

11. Sample 1
Batteries
included
 Would need an equation solver

12. Sample 2
• f[X]=2*X is equivalent to (f[X]==Y) <= (Y==2*x)
• Functions return only 1 value per key (aka dict())
• Functions can appear in expressions
• Resolution starts with the latest clause, and stops on first answer
• Support for aggregate functions : sum, min, max, …

13. Sample 3 Familiar tuple
notation
Memoized
 Faster
 Avoid infinite loop

14. Sample 4
Prefixed function
to query
Python classes
or SQL databases

15. Other pyDatalog features
• Runs on PyPy, Python 2, Python 3
• Accepts predicate definition written in Python
• For I/O, performance, …
• Thread-safe
• For use in multi-threaded web framework
• Multi-model : Switch from one Logic model (= set of clauses)
to another

16. Applications
Core technology Benefit Applications
The SLG resolution algorithm
determines the sequence of steps
to resolve a query.
Spreadsheet-programming : faster
iterations, fewer bugs, more
readable.
Rule-based expert systems for
pricing, tax calculation, access
right, robot control, intelligent
agent.
Input/output polymorphism. Maximise code reuse : shorter
program, simpler database query
language.
Cross-database queries, data
integration.
Intermediate results are memoized. Avoid re-calculation. Avoid infinite
loop.
Recursive algorithm on tree or
graph structures, natural language
processing, code analysis

17. Roadmap : Equation solver

18. Roadmap : Transactions
• Assert facts within transactions, with possible roll-back
• Use logic clauses to validate data operations
• Use logic clauses to define triggers (condition => action)
• Memoize results across queries within the same transaction
• Translate Datalog queries into SQL for server-side processing
Feedback, Help welcome !!

19. Roadmap : Performance
• Rewrite critical sections in C
• Exploit multi-threading in resolution engine
Feedback, Help welcome !!

20. Why Logic Programming in Python ?
Easy to learn
Batteries included
Query 11 SQL databases
Be productive
Be Readable
Use AI