input: Write a function to create a class in Python that can perform matrix operations including addition, subtraction, multiplication, and transpose. Include a method to initialize the matrix and another to print the matrix. Write assert statements to test the operations.
  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])
  
  assert str(Matrix(2, 2, [1, 2, 3, 4])) == "1 2 \n3 4 \n"
  assert str(Matrix(2, 2, [1, 2, 3, 4]).transpose()) == "1 3 \n2 4 \n"
  mat1 = Matrix(2, 2, [1, 2, 3, 4])
  mat2 = Matrix(2, 2, [5, 6, 7, 8])
  mat1.add(mat2)
  assert str(mat1) == "6 8 \n10 12 \n"
  mat1 = Matrix(2, 2, [1, 2, 3, 4])
  mat1.sub(mat2)
  assert str(mat1) == "-4 -4 \n-4 -4 \n"
  mat1 = Matrix(2, 2, [1, 2, 3, 4])
  mat1.mul(mat2)
  assert str(mat1) == "19 22 \n43 50 \n"
output: 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])