psamm.expression.affine – Affine expressions

Representations of affine expressions and variables.

These classes can be used to represent affine expressions and do manipulation and evaluation with substitutions of particular variables.

class psamm.expression.affine.Expression(*args)

Represents an affine expression (e.g. 2x + 3y - z + 5)

__add__(other)

Add expressions, variables or numbers

__div__(other)

Divide by scalar

__eq__(other)

Expression equality

__mul__(other)

Multiply by scalar

__sub__(other)

Subtract expressions, variables or numbers

__truediv__(other)

Divide by scalar

simplify()

Return simplified expression.

If the expression is of the form ‘x’, the variable will be returned, and if the expression contains no variables, the offset will be returned as a number.

substitute(mapping)

Return expression with variables substituted

>>> Expression('x + 2y').substitute(
...     lambda v: {'y': -3}.get(v.symbol, v))
Expression('x - 6')
>>> Expression('x + 2y').substitute(
...     lambda v: {'y': Variable('z')}.get(v.symbol, v))
Expression('x + 2z')

variables()

Return iterator of variables in expression

class psamm.expression.affine.Variable(symbol)

Represents a variable in an expression

Equality of variables is based on the symbol.

__eq__(other)

Check equality of variables

__ge__(other)

x.__ge__(y) <==> x>=y

__gt__(other)

x.__gt__(y) <==> x>y

__le__(other)

x.__le__(y) <==> x<=y

simplify()

Return simplified expression

The simplified form of a variable is always the variable itself.

>>> Variable('x').simplify()
Variable('x')

substitute(mapping)

Return expression with variables substituted

>>> Variable('x').substitute(lambda v: {'x': 567}.get(v.symbol, v))
567
>>> Variable('x').substitute(lambda v: {'y': 42}.get(v.symbol, v))
Variable('x')
>>> Variable('x').substitute(
...     lambda v: {'x': 123, 'y': 56}.get(v.symbol, v))
123

symbol

Symbol of variable

>>> Variable('x').symbol
'x'