input: from typing import List
  
  class Matrix:
      def __init__(self, m, n, lst):
          self.m = m
          self.n = n
          self.mat = []
  
          c = 0
          for i in range(self.m):
              a =[]
              for j in range(self.n):
                  a.append(lst[c])
                  c += 1
              self.mat.append(a)
  
      def __str__(self):
          output = ""
          for i in self.mat:
              for j in i:
                  output += str(j) + " "
              output += '\n'
          return output
  
      def add(self, mat2):
          for i in range(self.m):
              for j in range(self.n):
                  self.mat[i][j] += mat2.mat[i][j]
  
      def sub(self, mat2):
          for i in range(self.m):
              for j in range(self.n):
                  self.mat[i][j] -= mat2.mat[i][j]
  
      def mul(self, mat2):
          result = []
          for i in range(self.m):
              a =[]
              for j in range(mat2.n):
                  s = 0
                  for k in range(self.n):
                      s += self.mat[i][k] * mat2.mat[k][j]
                  a.append(s)
              result.append(a)
          self.mat = result
          self.m = len(result)
          self.n = len(result[0])
  
      def transpose(self):
          result = [[self.mat[j][i] for j in range(len(self.mat))] for i in range(len(self.mat[0]))]
          self.mat = result
          self.m = len(result)
          self.n = len(result[0])
  
      """
      You have a Matrix class that supports various operations like addition, subtraction, multiplication, and transpose. Now, extend this class to allow the matrix to be transformed by a scalar value. In other words, create a method that multiplies each element of the matrix by a given scalar.
  
      >>> mat = Matrix(2, 2, [1, 2, 3, 4])
      >>> mat.transform_by_scalar(2)
      >>> print(mat)
      2 4 
      6 8 
      """
output:     def transform_by_scalar(self, scalar):
          for i in range(self.m):
              for j in range(self.n):
                  self.mat[i][j] *= scalar