gotcha.py

# mutable list
def foobar(arg_string="abc", arg_list=[]): 
    print arg_string, arg_list 
    arg_string = arg_string + "xyz"
    arg_list.append("F")
 
 
for i in range(4): 
    foobar()
    
    
"""
  results
  abc []
  abc ['F']
  abc ['F', 'F']
  abc ['F', 'F', 'F']
"""


# late binding
def create_multipliers():
    return [lambda x : i * x for i in range(5)]
 
 
for multiplier in create_multipliers():
    print multiplier(2)
    
    
"""
   8
   8
   8
   8
   8
"""


class Foo(object):
    a = 1

foo = Foo()
foo.a = 2
Foo.a = 3
print(foo.a)
print(type(foo).a)