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)])
        print(self.adjMatrix)
        self.size = size

    def add_vertex(self):
        '''Method for adding a vertex into graph.'''

        for i in range(self.size):                              # iterate through vertices without the added one
            self.adjMatrix[i].append(0)                         # add zero for every vertex
                                                                # this zero represents connection with the added vertex
        self.size += 1                                          # increase the size of the graph
        self.adjMatrix.append([0 for i in range(self.size)])    # add zeros for added vertex
        print('Vertex added successfully.')                     # print info message

    def add_edge(self, vertex1, vertex2):
        '''Method for adding an edge between two vertices in graph.'''

        if vertex1 == vertex2:                          # if the vertices are same
            print('Both vertices are same!')            # print info message
        elif self.adjMatrix[vertex1][vertex2] == 1:     # if the vertices already have edge
            print('The edge already exists.')           # print info message
        else:                                           # the vertices have no edge and they are different
            self.adjMatrix[vertex1][vertex2] = 1        # add edge between the vertices
            self.adjMatrix[vertex2][vertex1] = 1        # add edge between the vertices also from the other side
            print('Edge is added successfully.')           # print info message

    def remove_edge(self, vertex1, vertex2):
        '''Method for removing an edge between two vetices in graph.'''

        if vertex1 == vertex2:                          # if the vertices are same
            print('Both vertices are same!')            # print info message
        elif self.adjMatrix[vertex1][vertex2] == 0:     # if the vertices have no edge
            print('There is no edge to be removed')     # print info message
        else:                                           # if the vertices are different and have an edge
            self.adjMatrix[vertex1][vertex2] = 0        # remove the edge between vertices
            self.adjMatrix[vertex2][vertex1] = 0        # remove the edge between vertices from the other side
            print('Edge is removed successfully.')         # print info message

    def print_matrix(self):
        '''https://thispointer.com/python-how-to-pad-strings-with-zero-space-or-some-other-character/ - ADAPTED
           Method for printing the graph in a matrix form.'''

        header = ''                                 # create empty string variable
        divLine = '--'                              # create line format
        for i in range(1, self.size+1):             # iterate through the vertices
            header = header + ' ' + str(i)          # add numbers of the vertices into header
        print("  ", header)                         # print the header
        print('  ', divLine.ljust(len(header),'-'))    # print the dividing line
        i=1                                         # set index to one
        for row in self.adjMatrix:                  # iterate through vertices
            print(i,'|',end=" ")                    # print number of the vertex and dividing line
            i+=1                                    # increment the index
            for val in row:                         # iterate through edges in every vertex
                print(val, end=" ")                 # print the edge value
            print('\n')                             # jump to a new line


def main():
    g = Graph(4)

    g.add_edge(0,1)
    g.add_edge(0,2)
    g.add_edge(1,2)
    g.add_edge(2,3)
    g.add_edge(1,3)

    g.remove_edge(1,3)

    g.add_vertex()
    g.add_vertex()


    g.print_matrix()


if __name__ == '__main__':
    main()