Python script to better understand Python Data Model

py_data_model.py

#!/usr/bin/python
"""
It is used to signify the absence of a value in many situations, e.g., it is returned from functions that don’t explicitly 
return anything.
"""
print 'None - Its truth value is False.'
bottle = None
if not bottle:
    print 'This proves that the truth value of None is False'
"""
Numeric methods and rich comparison methods may return this value if they do not implement the operation for the operands 
provided. (The interpreter will then try the reflected operation, or some other fallback, depending on the operator.)
reference: http://jcalderone.livejournal.com/32837.html
"""
print 'NotImplemented - Its truth value is True.'
wheel = NotImplemented
if wheel: 
    print 'This proves that the truth value of NotImplemented is True'
"""
It is used to indicate the presence of the ... syntax in a slice.
"""
print 'Ellipsis - Its truth value is True.'
dust = Ellipsis
if dust: 
    print 'This proves that the truth value of Ellipsis is True'
"""
An object’s mutability is determined by its type; for instance, numbers, strings and tuples are immutable, while dictionaries 
and lists are mutable.
"""
print 'List is mutable.'
def foo(numbers=[]): 
    numbers.append(9)
    print numbers

foo()
foo()
foo()
print 'This proves that List is mutable'
print 'Number is immutable.'
def increment(count=0): 
    count += 1 
    print count
    
increment()
increment()
increment()
print 'This proves that Number is immutable'
import time
print 'time.time() is immutable.'
def print_now(now=time.time()):
    print now
    
print_now()
print_now()
print_now()
print 'This proves that time.time() is immutable'