algebraixlib.undef module

Facilities for representing and working with the concept of “undefined”.

Most operations are not defined for all types of data: set operations may not be defined on couplets, multiset operations may not be defined on sets, and so on. When an operation is not defined for a given input, it returns the singleton Undef(). This return value can then be taken into account by the caller. In some cases it is an error, in other cases the result is simply ignored.

class algebraixlib.undef.Undef

Bases: object

A singleton class that represents the concept of “undefined”.

Instances of this class are not treated as a value by the operations in this library; specifically, it will never appear as the value of an Atom.

static __new__()

Override __new__ to create a singleton class.

__eq__(other)

Prevent comparisons on Undef; raise a TypeError.

__ne__(other)

Prevent comparisons on Undef; raise a TypeError.

__repr__()

Return the instance’s code representation.

__str__()

Return the instance’s string representation.

__hash__ = None

class algebraixlib.undef.RaiseOnUndef

Bases: object

Manage the level for make_or_raise_undef. Implemented as static class.

static get_level()

Return the current level for raising an UndefException.

The exception is raised if the level argument of make_or_raise_undef is less than or equal to the value returned here.

static set_level(temp_value)

Set the level for raising an UndefException temporarily to temp_value.

static reset()

Reset the level for raising an UndefException back to its initial value.

exception algebraixlib.undef.UndefException

Bases: Exception

This exception is raised when the level argument of make_or_raise_undef is less than or equal to the RaiseOnUndef level.

algebraixlib.undef.make_or_raise_undef(level=1)

Raise UndefException if level is less than or equal to the RaiseOnUndef level, otherwise return Undef().

Parameters:level – An integer >= 1. Default is 1.

Note

Use 1 (or no argument) for the cases that are most likely to be errors (like wrong argument types). Use higher numbers for cases that may return Undef() on purpose.