The following code:
--{--cut here--
#Purpose:
# Demonstrate class with __add__ and __mult__ methods
# to demonstrate shortestPath calculations.
#OriginalSource:
# ./shortestPath.py
#References:
# [1]
http://www.marinamele.com/2014/04/modifying-add-method-of-python-class.html
# [2]
https://docs.scipy.org/doc/numpy/reference/c-api.types-and-structures.html#c...
# [3]
https://www.abebooks.com/book-search/title/graphs-networks/author/carre-bern...
# Table 3.1, path algebra P2.
# [4] https://docs.python.org/3/library/abc.html
###########################################
import numpy as np
from abc import ABCMeta, abstractmethod
class PathAbstract(metaclass=ABCMeta):
@abstractmethod
def __repr__(self):
pass
@abstractmethod
def __add__(self, other):
pass
@abstractmethod
def __radd__(self, other):
pass
@abstractmethod
def __mul__(self, other):
pass
@abstractmethod
def __rmul__(self, other):
pass
class ShortestNull(PathAbstract):
'''Null object in ShortestPath algebra[3]'''
def __str__(self):
return "<0>"
def __repr__(self):
return self.__str__()
def __addreal__(self, other):
return other
def __add__(self, other):
return other
def __radd__(self, other):
return other
def __mulreal__(self, other):
return self
def __mul__(self, other):
return self
def __rmul__(self, other):
return self
class ShortestUnit(PathAbstract):
'''Unit object in ShortestPath algebra[3]'''
def __str__(self):
return "<1>"
def __repr__(self):
return self.__str__()
def __addreal__(self, other):
return self
def __add__(self, other):
return self
def __radd__(self, other):
return self
def __mulreal__(self, other):
return other
def __mul__(self, other):
return other
def __rmul__(self, other):
return other
class ShortestPath(PathAbstract):
def __init__(self, distance):
self.distance = distance
def __str__(self):
return "{0:4.1f}".format(self.distance)
def __repr__(self):
return self.__str__()
def __addreal__(self, other):
#paths composed of following shortest of self path or other path.
min_dist=min(self.distance,other.distance)
return ShortestPath(min_dist)
def __add__(self, other):
#paths composed of following shortest of self path or other path.
if(other == 0):
n=ShortestNull()
return n.__addreal__(self)
else:
return other.__addreal__(self)
def __radd__(self, other):
return self.__add__(other)
def __mulreal__(self, other):
#path composed of self path followed by other path.
min_dist=self.distance+other.distance
return ShortestPath(min_dist)
def __mul__(self, other):
return other.__mulreal__(self)
def __rmul__(self, other):
return other.__mulreal__(self)
d0=ShortestNull()
d1=ShortestUnit()
d2=ShortestPath(3)
d3=ShortestPath(6)
print(' d0=',d0,' d1=',d1,' d2=',d2,' d3=',d3)
print(' type(d0)=',type(d0).__name__)
d4=d0+d2+d3
print('d4=',d4)
d5=d2*d3
print('d5=',d5)
d6=d0*d2
print('d6=',d6)
d7=d1*d2
print('d7=',d7)
d8=d2*d0
print('d8=',d8)
d9=d2*d1
print('d9=',d9)
a=np.array([[ShortestNull,ShortestPath(12)],[ShortestPath(12),ShortestNull()]],dtype=object)
print('a=',a,sep='\n')
print('a[0]=',a[0],sep='\n')
print('a[0][0]=',a[0][0],sep='\n')
#a00mul=a[0][0]*a[0][0]
a00mul=a[0][0].__mul__(a[0][0])
print('a00mul=',a00mul,sep='\n')
#at=a.transpose()
#print('at=',at,sep='\n')
#aat=a.dot(at)
print('aat=',aat,sep='\n')
#mp=np.matmul(a,at)#this gives error about Object arrays not supported.
#print('mp=',mp)
--}--cut here--
When run by make, gives this result:
--{--cut here--
make -k
python3 shortestPathABC.py
d0= <0> d1= <1> d2= 3.0 d3= 6.0
type(d0)= ShortestNull
d4= 3.0
d5= 9.0
d6= <0>
d7= 3.0
d8= <0>
d9= 3.0
a=
[[