STD_3.py

class Graph(object):
    
    def __init__(self, size):
        self.adjMatrix = []
        for i in range(size):
            self.adjMatrix.append([0 for i in range(size)])
        self.size = size

    def addVer(self):
      '''
      Class method for adding vertices to the graph
      Input: No input
      Output: No output, class changes adjMatrix attribute instead
      '''
      for i in range(self.size):                          #repeat loop class attribute size number of times
        self.adjMatrix[i].append(0)                       #add 0 at the end of a list under the index i in adjMatrix list
      self.size += 1                                      #increase class attribute size by one
      self.adjMatrix.append([0] * self.size)              #append a list at the end of adjMatrix list consisting of 0 repeated class attribute size ammount of times
      
    def addEdg(self,vtx1,vtx2):
      '''
      Class method for adding an edge to the graph
      Input: No input
      Output: No output, class changes adjMatrix attribute instead      
      '''
      if self.adjMatrix[vtx1 - 1][vtx2 - 1] == 0:         #if an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 is equal to zero
        self.adjMatrix[vtx1 - 1][vtx2 - 1] = 1            #change value of an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 to 1
        self.adjMatrix[vtx2 - 1][vtx1 - 1] = 1            #change value of an element under index vtx1 - 1 in a list inside adjMatrix list under index vtx2 - 1 to 1
      else:                                               #if an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 is not equal to zero
        print('Edge already exist') 
        
    def remEdg(self,vtx1,vtx2):
      '''
      Class method for removing an edge from the graph
      Input: No input
      Output: No output, class changes adjMatrix attribute instead      
      '''
      if self.adjMatrix[vtx1 - 1][vtx2 - 1] != 0:         #if an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 is not equal to zero
        self.adjMatrix[vtx1 - 1][vtx2 - 1] = 0            #change value of an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 to 0
        self.adjMatrix[vtx2 - 1][vtx1 - 1] = 0            #change value of an element under index vtx1 - 1 in a list inside adjMatrix list under index vtx2 - 1 to 0
      else:                                               #if an element under index vtx2 - 1 in a list inside adjMatrix list under index vtx1 - 1 is equal to zero
        print('Edge does not exist')

    def printMat(self):
      '''
      Class method for printing out the graph as a matrix
      Input: No input
      Output: No output, class uses print statements instead      
      '''
      print("   ",end='')                                 #print blank space, do not go to next line after the print statement
      for i in range(len(self.adjMatrix)):                #repeat loop length of adjMatrix ammount of times
        print(i+1,end="  ")                               #print i incremented by one, at the end of print statement, leave blank space instead of going to the next line
      print("\n  ", "-" * (len(self.adjMatrix) * 3 - 2))  #go to the next line and place empty spaces there, then print "-" number of times equal to lenth of adjMatrix multiplied by 3, subtracting 2 from that product 
      curVer = 1                                          #set value of variable current vertex to 1
      for i in self.adjMatrix:                            #outer loop, for every list in adjMatrix
        print(curVer,end = "| ")                          #print value of curVer variable, then print | and spaces instead of going to the next line
        for j in i:                                       #inner loop, repeat for every element in the list i 
          print(j,end = "  ")                             #print element of a list j, and create a space instead of going to the next line
        print("\n")                                       #go to the next line
        curVer += 1                                       #increment the value of curVer variable by 1
        
def main():
    g = Graph(6)
    g.addVer()
    g.addEdg(1,2)
    g.addEdg(3,4)
    g.remEdg(1,2)
    print(g.adjMatrix)
    print("\n")
    g.printMat()   
if __name__ == '__main__':
    main()

#notes:
#we subtract 1 from v1 because vertices start from 1, and lists from 0
# we do not check if vertices are the same in addEdg as edge can go from ver1 to ver1
#in addEdg although comparison if self.adjMatrix[vtx1 - 1][vtx2 - 1] == 0 is not necessary, as replacing an edge would change 1 to 1, it would create need for unnecesary calculasions, and if our graph were weighted, overwrite the edge which would be better to do by a separate method