Source code for

.. module:: world
    :platform: Linux, Unix, Windows
    :synopsis: Provides classes for representing a world and its edges.

.. moduleauthor:: Robert Grant <>

import json

[docs]class World: """The nodes and edges of a particular problem. Each :class:`World` is created from a list of nodes, a length function, and optionally, a name and a description. Additionally, each :class:`World` has a UID. The length function must accept nodes as its first two parameters, and is responsible for returning the distance between them. It is the responsibility of the :func:`create_edges` to generate the required :class:`Edge`\s and initialize them with the correct *length* as returned by the length function. Once created, :class:`World` objects convert the actual nodes into node IDs, since solving does not rely on the actual data in the nodes. These are accessible via the :attr:`nodes` property. To access the actual nodes, simply pass an ID obtained from :attr:`nodes` to the :func:`data` method, which will return the node associated with the specified ID. :class:`Edge`\s are accessible in much the same way, except two node IDs must be passed to the :func:`data` method to indicate which nodes start and end the :class:`Edge`. For example: .. code-block:: python ids = world.nodes assert len(ids) > 1 node0 =[0]) node1 =[1]) edge01 =[0], ids[1]) assert edge01.start == node0 assert edge01.end == node1 The :func:`reset_pheromone` method provides an easy way to reset the pheromone levels of every :class:`Edge` contained in a :class:`World` to a given *level*. It should be invoked before attempting to solve a :class:`World` unless a "blank slate" is not desired. Also note that it should *not* be called between iterations of the :class:`Solver` because it effectively erases the memory of the :class:`Ant` colony solving it. :param list nodes: a list of nodes :param callable lfunc: a function that calculates the distance between two nodes :param str name: the name of the world (default is "world#", where "#" is the ``uid`` of the world) :param str description: a description of the world (default is None) """ uid = 0 def __init__(self, nodes, lfunc, **kwargs): self.uid = self.__class__.uid self.__class__.uid += 1 = kwargs.get('name', 'world{}'.format(self.uid)) self.description = kwargs.get('description', None) self._nodes = nodes self.lfunc = lfunc self.edges = self.create_edges() @property def nodes(self): """Node IDs.""" return list(range(len(self._nodes)))
[docs] def create_edges(self): """Create edges from the nodes. The job of this method is to map node ID pairs to :class:`Edge` instances that describe the edge between the nodes at the given indices. Note that all of the :class:`Edge`\s are created within this method. :return: a mapping of node ID pairs to :class:`Edge` instances. :rtype: :class:`dict` """ edges = {} for m in self.nodes: for n in self.nodes: a, b =, if a != b: edge = Edge(a, b, length=self.lfunc(a, b)) edges[m, n] = edge return edges
[docs] def reset_pheromone(self, level=0.01): """Reset the amount of pheromone on every edge to some base *level*. Each time a new set of solutions is to be found, the amount of pheromone on every edge should be equalized to ensure un-biased initial conditions. :param float level: amount of pheromone to set on each edge (default=0.01) """ for edge in self.edges.values(): edge.pheromone = level
[docs] def data(self, idx, idy=None): """Return the node data of a single id or the edge data of two ids. If only *idx* is specified, return the node with the ID *idx*. If *idy* is also specified, return the :class:`Edge` between nodes with indices *idx* and *idy*. :param int idx: the id of the first node :param int idy: the id of the second node (default is None) :return: the node with ID *idx* or the :class:`Edge` between nodes with IDs *idx* and *idy*. :rtype: node or :class:`Edge` """ try: if idy is None: return self._nodes[idx] else: return self.edges[idx, idy] except IndexError: return None
[docs]class Edge: """This class represents the link between starting and ending nodes. In addition to *start* and *end* nodes, every :class:`Edge` has *length* and *pheromone* properties. *length* represents the static, *a priori* information, whereas *pheromone* level represents the dynamic, *a posteriori* information. :param node start: the node at the start of the :class:`Edge` :param node end: the node at the end of the :class:`Edge` :param float length: the length of the :class:`Edge` (default=1) :param float pheromone: the amount of pheromone on the :class:`Edge` (default=0.1) """ def __init__(self, start, end, length=None, pheromone=None): self.start = start self.end = end self.length = 1 if length is None else length self.pheromone = 0.1 if pheromone is None else pheromone def __eq__(self, other): if isinstance(other, self.__class__): return self.__dict__ == other.__dict__ return False