what is doc string in python code example

Example: function description in python

def mySum(a: float, b: float) -> float:
  	"""
   mySum(a, b) Calculates the sum of two numbers
   
   example: mySum(1.0, 2.0) -> 3.0
   
   example: mySum(2.0, -1.5) -> 0.5
    
   :param: a: First number
   
   :param: b: Second Number
   
   :returns: sum of first and second number
    
   """
    
   return a+b		# Actual function body