Change Log

0.7.0: 2017-XX-XX – Class Based Walkers and Sorts


  • Removed option “quantified” in Solver (PR #377)
  • Removed deprecated CNFizer.printer method (PR #359)


  • Class-Based Walkers (PR #359):

    Walkers behavior is now defined in the class definition. Processing an AND node always calls walk_and. This makes it possible to subclass and override methods, but at the same time call the implementation of a super class, e.g.:

    def walk_and(...):
         return ParentWalker.walk_and(self, ....)

    The utility method Walker.super is provided to automatically handle the dispatch of a node to the correct walk_* function, e.g.,:

    def walk_bool_to_bool(...):
        return ParentWalker._super(self, ....)

    The method Walker.set_functions is deprecated, but kept for compatibility with old-style walkers. Using set_functions has the same effect as before. However, you cannot modify a subclass of a walker using set_functions. You should not be using set_functions anymore!

    The method Walker.set_handler is used to perform the same operation of set_function at the class level. The associated decorator @handles can be used to associate methods with nodetypes.

    These changes make it possible to extend the walkers from outside pySMT, without relying on hacks like the Dynamic Walker Factory (DWF). See examples/ for a detailed example.

  • Introduce the support for custom sorts (PySMTTypes) (PR #375)

    Two new classes are introduced: _Type and PartialType

    PartialType is used to represent the concept of SMT-LIB “define-sort”. The class _TypeDecl is used to represents a Type declaration, and as such cannot be used directly to instantiate a Symbol. This capture the semantics of declare-sort. A wrapper Type() is given to simplify its use, and making 0-arity sorts a special case. The following three statements are equivalent:

    Type("Colors", 0)
    _TypeDecl("Colors", 0)()

    In particular, the last case shows that instantiating a TypeDeclaration returns a PySMTType:

    Type(Pair, 2)(Int, Int)

    Type declarations and Type instances are memoized in the environment, and suitable shortucts have been introduced.

  • Add shortcuts.to_smtlib() to easily dump an SMT-LIB formula


  • Fixed assumption handling in the Boolector wrapper. Thanks to Alexey Ignatiev for contributing with this patch!
  • Fix cyclic imports (PR #406). Thanks to @rene-rex for reporting this.

0.6.1: 2016-12-02 – Portfolio and Coverage


  • Portfolio Solver (PR #284):

    Created Portfolio class that uses multiprocessing to solve the problem using multiple solvers. get_value and get_model work after a SAT query. Other artifacts (unsat-core, interpolants) are not supported. Factory.is_* methods have been extended to include portfolio key-word, and exported as is_* shortcuts. The syntax becomes:

    is_sat(f, portfolio=["s1", "s2"])
  • Coverage has been significantly improved, thus giving raise to some clean-up of the tests and minor bug fixes. Thanks to for providing free coverage analysis. (PR #353, PR #358, PR #372)

  • Introduce PysmtException, from which all exceptions must inherit. This also introduces hybrid exceptions that inherit both from the Standard Library and from PysmtException (i.e., PysmtValueError). Thanks to Alberto Griggio for suggesting this change. (PR #365)

  • Windows: Add support for installing Z3. Thanks to Samuele Gallerani for contributing this patch. (PR #385)

  • Arrays: Improved efficiency of array_value_get (PR #357)

  • Documentation: Thanks to the Hacktoberfest for sponsoring these activities:

    • Every function in now has a docstring! Thanks to Vijay Raghavan for contributing this patch. (PR #363)
    • Contributing information has been moved to the official documentation and prettyfied! Thanks to Jason Taylor Hodge for contributing this patch. (PR #339)
    • Add link to Google Group in . Thanks to @ankit01ojha for contributing this. (PR #345)
  • smtlibscript_from_formula(): Allow the user to specify a custom logic. Thanks to Alberto Griggio for contributing this patch. (PR #360)


  • MathSAT: Improve back-conversion performance by using MSAT_TAGS (PR #379)
  • MathSAT: Add LIA support for Quantifier Elimination
  • Removed: Solver.declare_variable and Solver.set_options (PR #369, PR #378)


  • CVC4:
    • Enforce BV Division by 0 to return a known value (0xFF) (PR #351)
    • Force absolute import of CVC4. Thanks to Alexey Ignatiev (@2sev) for reporting this issue. (PR #382)
  • MathSAT: Thanks to Alberto Griggio for contributing these patches
    • Fix assertions about arity of BV sign/zero extend ops. (PR #350, PR #351)
    • Report the error message generated by MathSAT when raising a SolverReturnedUnknownResultError (PR #355)
  • Enforce a single call to is_sat in non-incremental mode (PR #368). Thanks to @colinmorris for pointing out this issue.
  • Clarified Installation section and added example of call to `pysmt-install --env`. Thanks to Marco Roveri (@marcoroveri) for pointing this out.
  • SMT-LIB Parser:
    • Minor fixes highlighted by fuzzer (PR #376)
    • Fixed annotations parsing according to SMTLib rules (PR #374)
  • pysmt-install: Gracefully fail if GIT is not installed (PR #390) Thanks to Alberto Griggio for reporting this.
  • Removed dependency from internet connections when checking picosat version (PR #386)

0.6.0: 2016-10-09 – GMPY2 and Goodbye Recursion


  • Integer, Fraction and Numerals are now defined in pysmt.constants (see below for details). The breaking changes are:

    • Users should use pysmt.constants.Fraction, if they want to guarantee that the same type is being used (different types are automatically converted);
    • Methods from pysmt.utils moved to pysmt.constants;
    • Numerals class was moved from pysmt.numeral (that does not exist anymore).
  • Non-Recursive TreeWalker (PR #322)

    Modified TreeWalker to be non-recursive. The algorithm works by keeping an explicit stack of the walking functions that are now required to be generators. See pysmt.printer.HRPrinter for an example. This removes the last piece of recursion in pySMT !

  • Times is now an n-ary operator (Issue #297 / PR #304)

    Functions operating on the args of Times (e.g., rewritings) should be adjusted accordingly.

  • Simplified module pysmt.parsing into a unique file (PR #301)

    The pysmt.parsing module was originally divided in two files: and These files were removed and the parser combined into a unique file. Code importing those modules directly needs to be updated.

  • Use solver_options to specify solver-dependent options (PR #338):

    • MathSAT5Solver option ‘debugFile’ has been removed. Use the solver option: “debug_api_call_trace_filename”.
    • BddSolver used to have the options as keyword arguments (static_ordering, dynamic_reordering etc). This is not supported anymore.
  • Removed deprecated methods (PR #332):

    • FNode.get_dependencies (use FNode.get_free_variables)
    • FNode.get_sons (use FNode.get_args)
    • FNode.is_boolean_operator (use FNode.is_bool_op)
    • pysmt.test.skipIfNoSolverAvailable
    • pysmt.randomizer (not used and broken)


  • Support for GMPY2 to represent Fractions (PR #309).

    Usage of GMPY2 can be controlled by setting the env variable PYSMT_GMPY to True or False. By default, pySMT tries to use GMPY2 if installed, and fallbacks on Python’s Fraction otherwise.

  • Constants module: pysmt.constants (PR #309)

    This module provides an abstraction for constants Integer and Fraction, supporting different ways of representing them internally. Additionally, this module provides several utility methods:

    • is_pysmt_fraction
    • is_pysmt_integer
    • is_python_integer
    • is_python_rational
    • is_python_boolean

    Conversion can be achieved via:

    • pysmt_fraction_from_rational
    • pysmt_integer_from_integer
    • to_python_integer (handle long/int py2/py3 mismatch)
  • Add Version information (Issue #299 / PR #303)

    • pysmt.VERSION : A tuple containing the version information
    • pysmt.__version__ : String representation of VERSION (following PEP 440)
    • pysmt.git_version : A simple function that returns the version including git information. (pysmt-install) and gain a new –version option that uses git_version to display the version information.

  • Shortcuts: read_smtlib() and write_smtlib()

  • Docs: Completely Revised the documentation (PR #294)

  • Rewritings: TimesDistributor (PR #302)

    Perform distributivity on an N-ary Times across addition and subtraction.

  • SizeOracle: Add MEASURE_BOOL_DAG measure (PR #319)

    Measure the Boolean size of the formula. This is equivalent to replacing every theory expression with a fresh boolean variable, and measuring the DAG size of the formula. This can be used to estimate the Boolean complexity of the SMT formula.

  • PYSMT_SOLVERS controls available solvers (Issue #266 / PR #316):

    Using the PYSMT_SOLVER system environment option, it is possible to restrict the set of installed solvers that are actually accessible to pySMT. For example, setting PYSMT_SOLVER=”msat,z3” will limit the accessible solvers to msat and z3.

  • Protect FNodeContent.payload access (Issue #291 / PR 310)

    All methods in FNode that access the payload now check that the FNode instance is of the correct type, e.g.:

    FNode.symbol_name() checks that FNode.is_symbol()

    This prevents from accessing the payload in a spurious way. Since this has an impact on every access to the payload, it has been implemented as an assertion, and can be disabled by running the interpreter with -O.


  • Z3 Converter Improvements (PR #321):

    • Optimized Conversion to Z3 Solver Forward conversion is 4x faster, and 20% more memory efficient, because we work at a lower level of the Z3 Python API and do not create intermediate AstRef objects anymore. Back conversion is 2x faster because we use a direct dispatching method based on the Z3 OP type, instead of the big conditional that we were using previously.
    • Add back-conversion via SMT-LIB string buffer. Z3Converter.back_via_smtlib() performs back conversion by printing the formula as an SMT-LIB string, and parsing it back. For formulas of significant size, this can be drastically faster than using the API.
    • Extend back conversion to create new Symbols, if needed. This always raise a warning alerting the user that a new symbol is being implicitly defined.
  • OSX: Z3 and MathSAT can be installed with pysmt-install (PR #244)

  • MathSAT: Upgrade to 5.3.13 (PR #305)

  • Yices: Upgrade to 2.5.1

  • Better handling of solver options (PR #338):

    Solver constructor takes the optional dictionary solver_options of options that are solver dependent. It is thus possible to directly pass options to the underlying solver.


  • Fixed: Times back conversion in Z3 was binary not n-ary. Thanks to Ahmed Irfan for submitting the patch (PR #340, PR #341)
  • Fixed: Bug in array_value_assigned_values_map, returning the incorrect values for an Array constant value. Thanks to Daniel Ricardo dos Santos for pointing this out and submitting the patch.
  • Fixed: SMT-LIB define-fun serialization (PR #315)
  • Issue #323: Parsing of variables named bvX (PR #326)
  • Issue #292: Installers: Make dependency from pip optional (PR #300)
  • Fixed: Bug in MathSAT’s get_unsat_core (PR #331), that could lead to an unbounded mutual recursion. Thanks to Ahmed Irfan for reporting this (PR #331)

0.5.1: 2016-08-17 – NIRA and Python 3.5


  • Non Linear Arithmetic (NRA/NIA): Added support for non-linear, polynomial arithmetic. This thoery is currently supported only by Z3. (PR #282)
    • New operator POW and DIV
    • LIRA Solvers not supporting Non-Linear will raise the NonLinearError exception, while solvers not supporting arithmetics will raise a ConvertExpressionError exception (see
    • Algebraic solutions (e.g., sqrt(2) are represented using the internal z3 object – This is bound to change in the future.


  • Python 3.5: Full support for Python 3.5, all solvers are now tested (and working) on Python 3.5 (PR #287)
  • Improved installed solvers check (
    • –check now takes into account the bindings_dir and prints the version of the installed solver
    • Bindings are installed in different directories depending on the minor version of Python. In this way it is possible to use both Python 2.7 and 3.5.
    • There is a distinction btw installed solvers and solvers in the PYTHONPATH.
    • Qelim, Unsat-Core and Interpolants are also visualized (but not checked)
  • Support for reading compressed SMT-LIB files (.bz2)
  • Simplified HRPrinter code
  • Removed six dependency from type_checker (PR #283)
  • BddSimplifier (pysmt.simplifier.BddSimplifier): Uses BDDs to simplify the boolean structure of an SMT formula. (See (PR #286)


  • Yices: New wrapper supporting python 3.5 (
  • Yices: Upgrade to 2.4.2
  • SMT-LIB Wrapper: Improved interaction with subprocess (#298)


  • Bugfix in Z3Converter.walk_array_value. Thanks to Alberto Griggio for contributing this patch
  • Bugfix in DL Logic comparison (commit 9e9c8c)

0.5.0: 2016-06-09 – Arrays


  • MGSubstituter becomes the new default substitution method (PR #253)

    When performing substitution with a mapping like {a: b, Not(a), c}, Not(a) is considered before a. The previous behavior (MSSubstituter) would have substituted a first, and then the rule for Not(a) would not have been applied.

  • Removed argument user_options from Solver()


  • Added support for the Theory of Arrays.

    In addition to the SMT-LIB definition, we introduce the concept of Constant Array as supported by MathSAT and Z3. The theory is currently implemented for MathSAT, Z3, Boolector, CVC4.

    Thanks to Alberto Griggio, Satya Uppalapati and Ahmed Irfan for contributing through code and discussion to this feature.


  • Simplifier: Enable simplification if IFF with constant: e.g., (a <-> False) into !a

  • Automatically enable Infix Notation by importing (PR #267)

  • SMT-LIB: support for define-sort commands without arguments

  • Improved default options for shortcuts:

    • Factory.is_* sets model generation and incrementality to False;
    • Factory.get_model() sets model generation to True, and incrementality to False.
    • Factory.Solver() sets model generation and incrementality to True;
  • Improved handling of options in Solvers (PR #250):

    Solver() takes **options as free keyword arguments. These options are checked by the class SolverOptions, in order to validate that these are meaningful options and perform a preliminary validation to catch typos etc. by raising a ValueError exception if the option is unknown.

    It is now possible to do: Solver(name="bdd", dynamic_reordering=True)


  • rePyCUDD: Upgrade to 75fe055 (PR #262)
  • CVC4: Upgrade to c15ff4 (PR #251)
  • CVC4: Enabled Quantified logic (PR #252)


  • Fixed bug in Non-linear theories comparison
  • Fixed bug in reset behavior of CVC4
  • Fixed bug in BTOR handling of bitwidth in shifts
  • Fixed bug in BTOR’s get_value function
  • Fixed bug in BTOR, when operands did not have the same width after rewriting.

0.4.4: 2016-05-07 – Minor


  • BitVectors: Added support for infix notation
  • Basic performance optimizations


  • Boolector: Upgraded to version 2.2.0


  • Fixed bug in ExactlyOne args unpacking. Thanks to Martin @hastyboomalert for reporting this.

0.4.3: 2015-12-28 – Installers and HR Parsing


  • pysmt.parsing: Added parser for Human Readable expressions
  • pysmt-install: new installer engine
  • Most General Substitution: Introduced new Substituter, that performs top-down substitution. This will become the default in version 0.5.
  • Improved compliance with SMT-LIB 2 and 2.5
  • EagerModel can now take a solver model in input
  • Introduce new exception ‘UndefinedSymbolError’ when trying to access a symbol that is not defined.
  • Logic names can now be passed to shortcuts methods (e.g., is_sat) as a string


  • MathSAT: Upgraded to version 5.3.9, including support for new detachable model feature. Thanks to Alberto Griggio for contributing this code.
  • Yices: Upgraded to version 2.4.1
  • Shannon: Quantifier Elimination based on shannon expansion (shannon).
  • Improved handling of Context (‘with’ statement), exit and __del__ in Solvers.


  • Introduced decorator pysmt.test.skipIfNoSMTWrapper
  • Tests do note explicitely depend anymore on unittest module. All tests that need to be executable only need to import pysmt.test.main.


  • #184: MathSAT: Handle UF with boolean args Fixed incorrect handling of UF with bool arguments when using MathSAT. The converter now takes care of rewriting the formula.
  • #188: Auto-conversion of 0-ary functions to symbols
  • #204: Improved quoting in SMT-LIB output
  • Yices: Fixed a bug in push() method
  • Fixed bug in Logic name dumping for SMT-LIB
  • Fixed bug in Simplifier.walk_plus
  • Fixed bug in CNF Converter (Thanks to Sergio Mover for pointing this out)


  • Shows how to use multi-processing to perform parallel and asynchronous solving
  • Demonstrates how to perform SMT-LIB parsing, dumping and extension
  • Einstein Puzzle with example of debugging using UNSAT-Cores.

0.4.2: 2015-10-12 – Boolector


  • Boolector 2.1.1 is now supported
  • MathSAT: Updated to 5.3.8


  • EqualsOrIff: Introduced shortcut to handle equality and mismatch between theory and predicates atoms. This simply chooses what to use depending on the operands: Equals if Theory, Iff if predicates. Example usage in examples/
  • Environment Extensibility: The global classes defined in the Environment can now be replaced. This makes it much easier for external tools to define new FNode types, and override default services.
  • Parser Extensibility: Simplified extensibility of the parser by splitting the special-purpose code in the main loop in separate functions. This also adds support for escaping symbols when dealing with SMT-LIB.
  • AUTO Logic: Factory methods default to logics.AUTO, providing a smarter selection of the logic depending on the formula being solved. This impacts all is_* functions, get_model, and qelim.
  • Shell: Import BV32 and BVType by default, and enable infix notation
  • Simplified HRPrinter
  • Added AIG rewriting (rewritings.AIGer)


  • Fixed behavior of CNFizer.cnf_as_set()
  • Fixed issue #159: error in parsing let bindings that refer to previous let-bound symbols. Thanks to Alberto Griggio for reporting it!

0.4.1: 2015-07-13 – BitVectors Extension


  • BitVectors: Added Signed operators


  • Support for BitVectors added for Z3, CVC4, and Yices


  • SmartPrinting: Print expression by replacing sub-expression with custom strings.
  • Moved global environment initialization to Now internal functions do no need to import anymore, thus breaking some circular dependencies.


  • Started deprecation of get_dependencies and get_sons
  • Depreaced Randomizer and associated functions.

0.4.0: 2015-06-15 – Interpolation and BDDs


  • Craig interpolation support through Interpolator class, binary_interpolant and sequence_interpolant shortcuts. Current support is limited to MathSAT and Z3. Thanks to Alberto Griggio for implementing this!
  • Rewriting functions: nnf-ization, prenex-normalization and disjunctive/conjunctive partitioning.
  • get_implicant(): Returns the implicant of a satisfiable formula.
  • Improved support for infix notation.
  • Z3Model Iteration bugfix


  • Switched from pycudd wrapper to a custom re-entrant version called repycudd (
  • Added BDD-Based quantifier eliminator for BOOL theory
  • Added support for static/dynamic variable ordering
  • Re-implemented back-conversion avoiding recursion

0.3.0: 2015-05-01 – BitVectors/UnsatCores


  • Added initial support for BitVectors and QF_BV logic. Current support is limited to MathSAT and unsigned operators.


  • Two new quantifier eliminators for LRA using MathSAT API: Fourier-Motzkin (msat_fm) and Loos-Weisspfenning (msat_lw)
  • Yices: Improved handling of int/real precision


  • Unsat Cores: Unsat core extraction with dedicated shortcut get_unsat_core . Current support is limited to MathSAT and Z3
  • Added support for Python 3. The library now works with both Python 2 and Python 3.
  • QuantifierEliminator and qelim shortcuts, as well as the respective factory methods can now accept a ‘logic’ parameter that allows to select a quantifier eliminator instance supporting a given logic (analogously to what happens for solvers).
  • Partial Model Support: Return a partial model whenever possible. Current support is limited to MathSAT and Z3.
  • FNode.size(): Added method to compute the size of an expression using multiple metrics.

0.2.4: 2015-03-15 – PicoSAT


  • PicoSAT solver support


  • Iterative implementation of FNode.get_free_variables(). This also deprecates FNode.get_dependencies().


  • Fixed bug (#48) in pypi package, making pysmt-install (and other commands) unavailable. Thanks to Rhishikesh Limaye for reporting this.

0.2.3: 2015-03-12 – Logics Refactoring


  • script to automate the installation of supported solvers.
  • get_logic() Oracle: Detects the logic used in a formula. This can now be used in the shortcuts (_is_sat()_, _is_unsat()_, _is_valid()_, and _get_model()_) by choosing the special logic pysmt.logics.AUTO.
  • Expressions: Added Min/Max operators.
  • SMT-LIB: Substantially improved parser performances. Added explicit Annotations object to deal with SMT-LIB Annotations.
  • Improved iteration methods on EagerModel

Backwards Incompatible Changes:

  • The default logic for Factory.get_solver() is now the most generic quantifier free logic supported by pySMT (currently, QF_UFLIRA). The factory not provides a way to change this default.
  • Removed option _quantified_ from all shortcuts.

0.2.2: 2015-02-07 – BDDs


  • pyCUDD to perform BDD-based reasoning


  • Dynamic Walker Function: Dynamic Handlers for new node types can now be registered through the environment (see Environment.add_dynamic_walker_function).

0.2.1: 2014-11-29 – SMT-LIB


  • Yices 2
  • Generic Wrapper: enable usage of any SMT-LIB compatible solver.


  • SMT-LIB parsing
  • Changed internal representation of FNode
  • Multiple performance improvements
  • Added configuration file

0.2.0: 2014-10-02 – Beta release.

Theories: LIRA Solvers: CVC4 General:

  • Type-checking
  • Definition of SMT-LIB logics
  • Converted the DAGWalker from recursive to iterative
  • Better handling of errors during formula creation and solving
  • Preferences among available solvers.


  • Option ‘quantified’ within Solver() and all related methods will be removed in the next release.

Backwards Incompatible Changes:

  • Renamed the module pysmt.types into pysmt.typing, to avoid conflicts with the Python Standard Library.

0.1.0: 2014-03-10 – Alpha release.

Theories: LIA, LRA, RDL, EUF Solvers: MathSAT, Z3 General Functionalities:

  • Formula Manipulation: Creation, Simplification, Substitution, Printing
  • Uniform Solving for QF formulae
  • Unified Quantifier Elimination (Z3 support only)

0.0.1: 2014-02-01 – Initial release.