# Source code for orion.algo.base

```# -*- coding: utf-8 -*-
"""
Base Search Algorithm
=====================

Formulation of a general search algorithm with respect to some objective.
Algorithm implementations must inherit from `orion.algo.base.OptimizationAlgorithm`.

"""
import hashlib
import logging
from abc import ABCMeta, abstractmethod

from orion.core.utils import Factory

log = logging.getLogger(__name__)

def infer_trial_id(point):
"""Compute a hashing of a point"""
return hashlib.md5(str(list(point)).encode("utf-8")).hexdigest()

# pylint: disable=too-many-public-methods
[docs]class BaseAlgorithm(object, metaclass=ABCMeta):
"""Base class describing what an algorithm can do.

Parameters
----------
space : `orion.algo.space.Space`
Definition of a problem's parameter space.
kwargs : dict
Tunable elements of a particular algorithm, a dictionary from
hyperparameter names to values.

Notes
-----
We are using the No Free Lunch theorem's [1]_[3]_ formulation of an
`BaseAlgorithm`.
We treat it as a part of a procedure which in each iteration suggests a
sample of the parameter space of the problem as a candidate solution and observes
the results of its evaluation.

**Developer Note**: Each algorithm's complete specification, i.e.  implementation of its methods
and parameters of its own, lies in a separate concrete algorithm class, which must be an
**immediate** subclass of `BaseAlgorithm`. [The reason for this is current implementation of
`orion.core.utils.Factory` metaclass which uses `BaseAlgorithm.__subclasses__()`.] Second, one
must declare an algorithm's own parameters (tunable elements which could be set by
configuration). This is done by passing them to `BaseAlgorithm.__init__()` by calling Python's
super with a `Space` object as a positional argument plus algorithm's own parameters as keyword
arguments. The keys of the keyword arguments passed to `BaseAlgorithm.__init__()` are interpreted
as the algorithm's parameter names. So for example, a subclass could be as simple as this
(regarding the logistics, not an actual algorithm's implementation):

Examples
--------
.. code-block:: python
:linenos:
:emphasize-lines: 7

from orion.algo.base import BaseAlgorithm
from orion.algo.space import (Integer, Space)

class MySimpleAlgo(BaseAlgorithm):

def __init__(self, space, multiplier=1, another_param="a string param"):
super().__init__(space, multiplier=multiplier, another_param=another_param)

def suggest(self, num=1):
print(self.another_param)
return list(map(lambda x: tuple(map(lambda y: self.multiplier * y, x)),
self.space.sample(num)))

def observe(self, points, results):
pass

dim = Integer('named_param', 'norm', 3, 2, shape=(2, 3))
s = Space()
s.register(dim)

algo = MySimpleAlgo(s, 2, "I am just sampling!")
algo.suggest()

References
----------
.. [1] D. H. Wolpert and W. G. Macready, “No Free Lunch Theorems for Optimization,”
IEEE Transactions on Evolutionary Computation, vol. 1, no. 1, pp. 67–82, Apr. 1997.
.. [2] W. G. Macready and D. H. Wolpert, “What Makes An Optimization Problem Hard?,”
Complexity, vol. 1, no. 5, pp. 40–46, 1996.
.. [3] D. H. Wolpert and W. G. Macready, “No Free Lunch Theorems for Search,”
Technical Report SFI-TR-95-02-010, Santa Fe Institute, 1995.

"""

requires_type = None
requires_shape = None
requires_dist = None

def __init__(self, space, **kwargs):
log.debug(
"Creating Algorithm object of %s type with parameters:\n%s",
type(self).__name__,
kwargs,
)
self._trials_info = {}  # Stores Unique Trial -> Result
self._space = space
self._param_names = list(kwargs.keys())
# Instantiate tunable parameters of an algorithm
for varname, param in kwargs.items():
# Check if tunable element is another algorithm
if isinstance(param, dict) and len(param) == 1:
subalgo_type = list(param)[0]
subalgo_kwargs = param[subalgo_type]
if isinstance(subalgo_kwargs, dict):
param = OptimizationAlgorithm(subalgo_type, space, **subalgo_kwargs)
elif (
isinstance(param, str)
and param.lower() in OptimizationAlgorithm.typenames
):
# pylint: disable=too-many-function-args
param = OptimizationAlgorithm(param, space)
elif varname == "seed":
self.seed_rng(param)

setattr(self, varname, param)

[docs]    def seed_rng(self, seed):
"""Seed the state of the random number generator.

:param seed: Integer seed for the random number generator.

.. note:: This methods does nothing if the algorithm is deterministic.
"""
pass

@property
def state_dict(self):
"""Return a state dict that can be used to reset the state of the algorithm."""
return {"_trials_info": self._trials_info}

[docs]    def set_state(self, state_dict):
"""Reset the state of the algorithm based on the given state_dict

:param state_dict: Dictionary representing state of an algorithm
"""
self._trials_info = state_dict.get("_trials_info")

[docs]    @abstractmethod
def suggest(self, num=1):
"""Suggest a `num` of new sets of parameters.

Parameters
----------
num: int, optional
Number of points to suggest. Defaults to 1.

Returns
-------
list of points or None
A list of lists representing points suggested by the algorithm. The algorithm may opt
out if it cannot make a good suggestion at the moment (it may be waiting for other
trials to complete), in which case it will return None.

Notes
-----
New parameters must be compliant with the problem's domain `orion.algo.space.Space`.

"""
pass

[docs]    def observe(self, points, results):
"""Observe the `results` of the evaluation of the `points` in the
process defined in user's script.

Parameters
----------
points : list of tuples of array-likes
Points from a `orion.algo.space.Space`.
Evaluated problem parameters by a consumer.
results : list of dicts
Contains the result of an evaluation; partial information about the
black-box function at each point in `params`.

Result
------
objective : numeric
Evaluation of this problem's objective function.
gradient : 1D array-like, optional
Contains values of the derivatives of the `objective` function
with respect to `params`.
constraint : list of numeric, optional
List of constraints expression evaluation which must be greater
or equal to zero by the problem's definition.

"""
for point, result in zip(points, results):
point_id = infer_trial_id(point)

if point_id not in self._trials_info:
self._trials_info[point_id] = (point, result)

@property
def is_done(self):
"""Return True, if an algorithm holds that there can be no further improvement.
By default, the cardinality of the specified search space will be used to check
if all possible sets of parameters has been tried.
"""
if len(self._trials_info) >= self.space.cardinality:
return True

if len(self._trials_info) >= getattr(self, "max_trials", float("inf")):
return True

return False

[docs]    def score(self, point):  # pylint:disable=no-self-use,unused-argument
"""Allow algorithm to evaluate `point` based on a prediction about
this parameter set's performance.

By default, return the same score any parameter (no preference).

:returns: A subjective measure of expected perfomance.
:rtype: float

"""
return 0

[docs]    def judge(self, point, measurements):  # pylint:disable=no-self-use,unused-argument
"""Inform an algorithm about online `measurements` of a running trial.

:param point: A tuple which specifies the values of the (hyper)parameters
used to execute user's script with.

This method is to be used as a callback in a client-server communication
between user's script and a orion's worker using a `BaseAlgorithm`.
Data returned from this method must be serializable and will be used as
a response to the running environment. Default response is None.

.. note:: Calling algorithm to `judge` a `point` based on its online
`measurements` will effectively change a state in the algorithm (like
a reinforcement learning agent's hidden state or an automatic early
stopping mechanism's regression), which it may change the value of
the property `should_suspend`.

:returns: None or a serializable dictionary containing named data

"""
return None

@property
def should_suspend(self):
"""Allow algorithm to decide whether a particular running trial is still
worth to complete its evaluation, based on information provided by the
`judge` method.

"""
return False

@property
def configuration(self):
"""Return tunable elements of this algorithm in a dictionary form
appropriate for saving.

"""
dict_form = dict()
for attrname in self._param_names:
if attrname.startswith("_"):  # Do not log _space or others in conf
continue
attr = getattr(self, attrname)
if isinstance(attr, BaseAlgorithm):
attr = attr.configuration
dict_form[attrname] = attr

return {self.__class__.__name__.lower(): dict_form}

@property
def space(self):
"""Domain of problem associated with this algorithm's instance."""
return self._space

@space.setter
def space(self, space_):
"""Propagate changes in defined space to possibly nested algorithms."""
self._space = space_
for attr in self.__dict__.values():
if isinstance(attr, BaseAlgorithm):
attr.space = space_

# pylint: disable=too-few-public-methods,abstract-method
class OptimizationAlgorithm(BaseAlgorithm, metaclass=Factory):
"""Class used to inject dependency on an algorithm implementation."""

pass
```