old_contents: def climb_stairs(n: int) -> int:
    """
    LeetCdoe No.70: Climbing Stairs
    Distinct ways to climb a n step staircase where
    each time you can either climb 1 or 2 steps. 
  
    Args:
        n: number of steps of staircase
  
    Returns:
        Distinct ways to climb a n step staircase 
  
    Raises:
        AssertionError: n not positive integer
  
    >>> climb_stairs(3) 
    3
    >>> climb_stairs(1)
    1
    """
    assert isinstance(n,int) and n > 0, "n needs to be positive integer, your input {0}".format(0)
    if n == 1: return 1 
    dp = [0]*(n+1)
    dp[0], dp[1] = (1, 1)
    for i in range(2,n+1): 
        dp[i] = dp[i-1] + dp[i-2]
    return dp[n]
  
new_contents: #!/usr/bin/env python3
  
  
  def climb_stairs(n: int) -> int:
      """
      LeetCdoe No.70: Climbing Stairs
      Distinct ways to climb a n step staircase where
      each time you can either climb 1 or 2 steps.
  
      Args:
          n: number of steps of staircase
  
      Returns:
          Distinct ways to climb a n step staircase
  
      Raises:
          AssertionError: n not positive integer
  
      >>> climb_stairs(3)
      3
      >>> climb_stairs(1)
      1
      >>> climb_stairs(-7)  # doctest: +ELLIPSIS
      Traceback (most recent call last):
          ...
      AssertionError: n needs to be positive integer, your input -7
      """
      fmt = "n needs to be positive integer, your input {}"
      assert isinstance(n, int) and n > 0, fmt.format(n)
      if n == 1:
          return 1
      dp = [0] * (n + 1)
      dp[0], dp[1] = (1, 1)
      for i in range(2, n + 1):
          dp[i] = dp[i - 1] + dp[i - 2]
      return dp[n]
  
  
  if __name__ == "__main__":
      import doctest
  
      doctest.testmod()
  
subject: Fix error message and format with python/black (#1025)