Исключения

2.7.1.py

# -*- encoding: utf-8 -*-
"""
Базовый синтаксис
"""

try:
    num = float(raw_input("\nEnter a number: "))
except(ValueError):
    print "That was not a number!" 
else:
    print "You entered the number", num     

2.7.2.py

# -*- encoding: utf-8 -*-
"""
Вложенная обработка
"""

try:
    try: 1/0
    except: 
       print "caught an exception" 
except ZeroDivisionError:
    print "caught divide-by-0 attempt" 

2.7.3.py

# -*- encoding: utf-8 -*-
"""
Инструкция finally
"""

try:
     raise KeyboardInterrupt
finally:
     print 'Goodbye, world!'

2.7.4.py

# -*- encoding: utf-8 -*-
"""
Возбуждение исключения
"""

def err():
    raise IndexError

def aFunction():
    try:
        err()
    except IndexError:
        print 'caught an index error!'
    else:
        print 'no error caught...'

if __name__ == '__main__': 
    aFunction()