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


print x[:10]
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]


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 sum(x)
99990000


print sum(y)
99990000


print sum(x)
99990000


print sum(y)
0


y = (2*x for x in range(10000))
print sum(y)
99990000


print sum(y)
0


d = {"joe":6, "moe":10, "zhou":3}
print d.keys()
['zhou', 'joe', 'moe']


print d.values()
[3, 6, 10]
print d.items()
[('zhou', 3), ('joe', 6), ('moe', 10)]


print d.iteritems()
<dictionary-itemiterator object at 0x0000000003FEE188>

for x in d.iteritems():
    print x
    
('zhou', 3)

('joe', 6)

('moe', 10)


y = d.iteritems()
for x in y:
    print x
    
('zhou', 3)

('joe', 6)

('moe', 10)


for s in y:
    print s
    
# nothing is printed


y = (2*x for x in range(10000))
print type(y)
<type 'generator'>


print y
<generator object <genexpr> at 0x0000000003FE4120>


for x in y:
    print x
    
0

2

4
... lots of numbers