举例介绍Python中的25个隐藏特性

def foo(x, y):
  print x, y
 
alist = [1, 2]
adict = {'x': 1, 'y': 2}
 
foo(*alist) # 1, 2
foo(**adict) # 1, 2

>>> x = 3
>>> 1 < x < 5
True
>>> 4 > x >=3
True

>>> def foo(x=[]):
...   x.append(1)
...   print x
...
>>> foo()
[1]
>>> foo()
[1, 1]

>>> def foo(x=None):
...   if x is None:
...     x = []
...   x.append(1)
...   print x
...
>>> foo()
[1]
>>> foo()
[1]
>>>

sum[value] = sum.get(value, 0) + 1

>>> print "Hello %(name)s !" % {'name': 'James'}
Hello James !
>>> print "I am years %(age)i years old" % {'age': 18}
I am years 18 years old

>>> print "Hello {name} !".format(name="James")
Hello James !

>>> for i in (1, 3, 5):
...   if i % 2 == 0:
...     break
... else:
...   print "var i is always an odd"
...
var i is always an odd
>>>

>>> class Dict(dict):
...  def __missing__(self, key):
...   self[key] = []
...   return self[key]
...
>>> dct = Dict()
>>> dct["foo"].append(1)
>>> dct["foo"].append(2)
>>> dct["foo"]
[1, 2]

>>> from collections import defaultdict
>>> dct = defaultdict(list)
>>> dct["foo"]
[]
>>> dct["bar"].append("Hello")
>>> dct
defaultdict(<type 'list'>, {'foo': [], 'bar': ['Hello']})

>>> Name = "Wang" "Hong"
>>> Name
'WangHong'

>>> Name = "Wang" \
... "Hong"
>>> Name
'WangHong'
10. Python解释器中的”_”
 
>>> range(4)
[0, 1, 2, 3]
>>> _
[0, 1, 2, 3]

import this

>>> [(i, j) for i in range(3) for j in range(i)]
[(1, 0), (2, 0), (2, 1)]
14. try/except/else
 
try:
 put_4000000000_volts_through_it(parrot)
except Voom:
 print "'E's pining!"
else:
 print "This parrot is no more!"
finally:
 end_sketch()

>>> print >> open("somefile", "w+"), "Hello World"

Python 3.2 (r32:88445, Oct 20 2012, 14:09:50)
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> ...
Ellipsis

>>> class C(object):
... def __getitem__(self, item):
...  return item
...
>>> C()[1:2, ..., 3]
(slice(1, 2, None), Ellipsis, 3)
>>>

>>> a, b, *rest = range(10)
>>> a
0
>>> b
1
>>> rest
[2, 3, 4, 5, 6, 7, 8, 9]
>>>

>>> first, second, *rest, last = range(10)
>>> first
0
>>> second
1
>>> last
9
>>> rest
[2, 3, 4, 5, 6, 7, 8]

>>> pow(4, 2, 2)
0
>>> pow(4, 2, 3)
1

>>> lst = ["a", "b", "c"]
>>> list(enumerate(lst, 1))
[(1, 'a'), (2, 'b'), (3, 'c')]

>>> set([1,2,3])

>>> {1,2,3}
set([1, 2, 3])

>>> a = [1, 2, 3, 4, 5, 6, 7]
>>> a[1:4] = []
>>> a
[1, 5, 6, 7]

>>> a = [0, 1, 2, 3, 4, 5, 6, 7]
>>> del a[::2]
>>> a
[1, 3, 5, 7]

>>> isinstance(1, (float, int))
True
>>> isinstance(1.3, (float, int))
True
>>> isinstance("1.3", (float, int))
False

>>> isinstance("1.3", (float, int, str))
True

>>> a, b = {}, {}
>>> a['b'] = b
>>> b['a'] = a
>>> a
{'b': {'a': {...}}}

>>> a, b = [], []
>>> a.append(b)
>>> b.append(a)
>>> a
[[[...]]]

>>> int(u'1234')
1234

 
>>> class O(object):pass
...
>>> o = O()
>>> setattr(o, "can't touch this", 123)
>>> o.can't touch this
 File "<stdin>", line 1
  o.can't touch this
           ^
SyntaxError: EOL while scanning string literal
>>>
 File "<stdin>", line 1
  o.can't touch this
           ^
SyntaxError: EOL while scanning string literal