Constant functions¶

class sage.misc.constant_function.ConstantFunction[source]¶

Bases: SageObject

A class for function objects implementing constant functions.

EXAMPLES:

Sage

sage: f = ConstantFunction(3)
sage: f
The constant function (...) -> 3
sage: f()
3
sage: f(5)
3

Python

>>> from sage.all import *
>>> f = ConstantFunction(Integer(3))
>>> f
The constant function (...) -> 3
>>> f()
3
>>> f(Integer(5))
3

Such a function could be implemented as a lambda expression, but this is not (currently) picklable:

Sage

sage: g = lambda x: 3
sage: try:
....:     loads(dumps(g))
....: except Exception as e:
....:     if 'PicklingError' in str(type(e).__name__):
....:         print('PicklingError Caught')
PicklingError Caught
sage: f == loads(dumps(f))
True

Python

>>> from sage.all import *
>>> g = lambda x: Integer(3)
>>> try:
...     loads(dumps(g))
... except Exception as e:
...     if 'PicklingError' in str(type(e).__name__):
...         print('PicklingError Caught')
PicklingError Caught
>>> f == loads(dumps(f))
True

Also, in the long run, the information that this function is constant could be used by some algorithms.

Todo

Should constant functions have unique representation?
Should the number of arguments be specified in the input?
Should this go into sage.categories.maps? Then what should be the parent (e.g. for lambda x: True)?