Recursive String Reversal in Python.

reverse_string_recursively.py

# Recursively returns a reversed copy of the given string.
# An exercise from MITx: 6.00.1x Introduction to Computer Science and Programming Using Python.

def reverseString(aStr):
  """
  Given a string, recursively returns a reversed copy of the string.
  For example, if the string is 'abc', the function returns 'cba'.
  The only string operations you are allowed to use are indexing,
  slicing, and concatenation.
    
  aStr: a string
  returns: a reversed string
  """
  def reverseStringRecur(aStr):
    if not aStr or len(aStr) == 0:
      return aStr
    else:
      return aStr[-1] + reverseString(aStr[0:-1])
  if type(aStr) == type(""):
    return reverseStringRecur(aStr)
  else:
    raise TypeError("`aStr' must be a string!")