cf.Comparison

class cf.Comparison(relation, value, units=None)

Bases: object

Create an object for storing a comparison expression.

A comparison expression comprises a relation (such as ‘less than’) and a value (any object capable of being related to with the standard comparison operators). These are stored in the relation and value attributes respectively.

The comparison is evaluated for an arbitrary object with the evaluate method.

Valid relations are:

Relation	Description
‘lt’	Strictly less than
‘le’	Less than or equal
‘gt’	Strictly greater than
‘ge’	Greater than or equal
‘eq’	Equals (within a tolerance)
‘ne’	Not equal to (within a tolerance)
‘inside’	Inside a given range (range bounds included)
‘outside’	Outside a given range (range bounds excluded)

As a convenience, for each relation in the above list there is an identically named function which returns the appropriate Comparison object.

Examples

>>> c = cf.Comparison('le', 5)
>>> c.evaluate(4)
True
>>> c.evaluate(5)
True

>>> c = lt(5)
>>> c.evaluate(4)
True

>>> c = cf.Comparison('inside', (1,2))
>>> a = numpy.arange(4)
>>> c.evaluate(a)
array([False,  True,  True, False], dtype=bool)
>>> (a >= 1) & (a <= 2)
array([False,  True,  True, False], dtype=bool)

Initialization

Parameters :

relation : str

The comparison operator type.

value : object

The value on the right hand side of the comparison operation.

units : str or Units, optional

The units of value. By default, the same units as the left hand side of the comparison operation are assumed.

copy()

Return a deep copy.

Equivalent to copy.deepcopy(c).

Returns :

out :

The deep copy.

Examples

>>> c.copy()

dump(id=None)

Return a string containing a full description of the instance.

Parameters :

id : str, optional

Set the common prefix of component names. By default the instance’s class name is used.

Returns :

out : str

A string containing the description.

Examples

>>> x = c.dump()
>>> print c.dump()
>>> print c.dump(id='comparison1')

evaluate(x)

Evaluate the comparison expression for a given object.

Parameters :

x : object

The object for the left hand side of the comparison expression.

Returns :

out :

The output of the comparison given by the relation attribute with x on the left hand side and the value attribute on the right hand side.

Examples

>>> c = cf.Comparison('lt', 5.5)
>>> c.evaluate(6)
False

>>> c = cf.Comparison('inside', (1,2))
>>> array = numpy.arange(4)
>>> array
array([0, 1, 2, 3])
>>> c.evaluate(array)
array([False,  True,  True, False], dtype=bool)