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Arguments in python are passed as an assignment. This assignment creates an object that has no relationship between an argument name in source and target. The procedure to write the function using call by reference includes:
The tuple result can be returned to the object which called it. The example below shows it:
def function(a, b):
a = 'value'
b = b + 1
# a and b are local variables that are used to assign the new objects
return a, b
# This is the function that is used to return the value stored in b
• The use of global variables allows the function to be called as reference but this is not the safe method to call any function.
• The use of mutable (they are the classes that consists of changeable objects) objects are used to pass the function by reference.
def function(a):
a[0] = 'string'
a[1] = a[1] + 1
# The ‘a’ array give reference to the mutable list and it changes the changes that are shared
args = ['string', 10]
func1(args)
print args[0], args[1]
#This prints the value stored in the array of ‘a’

Delegation is a technique that is used in object oriented programming. This is used to show the object and the behavior of the methods that are used. The class can be created to provide an implementation of the method that allows the method to be referenced. The delegate is having the parameter and the return value in an object. It also allows the methods to be passed as parameters and allow the defining of the callback methods that can be grouped together in multiple methods. These methods can be called from a single event. The example shows a class that captures the behavior of the file and converts data from lower to uppercase.
class upcase:
def __init__(self, out):
self._out = out
def write(self, s):
self._outfile.write(s.upper())
def __getattr__(self, name):
return getattr(self._out, name)
The write() method that is used in the upcase class converts the string to the uppercase before calling another method. The delegation is being given using the self.__outfile object.

LIST comprehensions features were introduced in Python version 2.0, it creates a new list based on existing list.
It maps a list into another list by applying a function to each of the elements of the existing list.
List comprehensions creates lists without using map() , filter() or lambda form.