input: Write a function to optimize a Python program that processes a 2d array and stores the transpose output in a new array.
  
  def transpose(A):
      n = len(A)
      m = len(A[0])
      B = [[0 for x in range(n)] for x in range(m)]
      for i in range(n):
          for j in range(m):
              B[j][i] = A[i][j]
      return B
  
  assert transpose([[1, 2, 3], [4, 5, 6]])==[[1, 4], [2, 5], [3, 6]]
  assert transpose([[1, 2], [3, 4], [5, 6]])==[[1, 3, 5], [2, 4, 6]]
  assert transpose([[1]])==[[1]]
  assert transpose([[]])==[[]]
  assert transpose([])==[]
output: def transpose(A):
      if not A:
          return []
      n = len(A)
      m = len(A[0])
      B = [[A[i][j] for i in range(n)] for j in range(m)]
      return B