x = [2*x for x in range(10000)]
print len(x)
10000

print x[:20]
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38]


print x[9990:]
[19980, 19982, 19984, 19986, 19988, 19990, 19992, 19994, 19996, 19998]


y = (2*x for x in range(10000))
print len(y)
Traceback (most recent call last):
  File "C:\Users\Susan\AppData\Local\Enthought\Canopy\App\appdata\canopy-2.1.3.3542.win-x86_64\lib\site-packages\IPython\core\interactiveshell.py", line 2885, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-7-6c8f20a5bcf6>", line 1, in <module>
    print len(y)
TypeError: object of type 'generator' has no len()

print y
<generator object <genexpr> at 0x0000000003EF8F78>


print sum(x)
99990000


print sum(y)
99990000


print sum(x)
99990000


print sum(y)
0


d = {"sam":3, "mary":10, "zhou":5}
print d.keys()
['zhou', 'mary', 'sam']


print d.values()
[5, 10, 3]


print d.items()
[('zhou', 5), ('mary', 10), ('sam', 3)]


print d.iteritems()
<dictionary-itemiterator object at 0x0000000003F3F098>


for x in d.iteritems():
    print x
    
('zhou', 5)

('mary', 10)

('sam', 3)


for x in d.iteritems():
    print x
    
('zhou', 5)

('mary', 10)

('sam', 3)


y = d.iteritems()
for x in y:
    print x
    
('zhou', 5)

('mary', 10)

('sam', 3)


for x in y:
    print x

# nothing printed