Pythonの文法と戯れる

pythonの文法の興味深いところをメモってみました。

• リストのスライス

>>> list = [1, 2, 3, 4, 5]
>>> list[1]
2
>>> list[1:]
[2, 3, 4, 5]
>>> list[1:3]
[2, 3]
>>> list[:3]
[1, 2, 3]
>>> list[:]
[1, 2, 3, 4, 5]
>>> list[-1]
5
>>> list[-2]
4
>>> list[-2:]
[4, 5]
>>> list[:-2]
[1, 2, 3]
>>> list[-2:-1]
[4]
>>> list[0]
1
>>> list[-0]
1
>>> list[+0]
1

• タプルの連結

>>> (1, 2, 3) + 4
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
TypeError: can only concatenate tuple (not "int") to tuple

>>> (1, 2, 3) + (4)
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
TypeError: can only concatenate tuple (not "int") to tuple

>>> (1, 2, 3) + (4,)
(1, 2, 3, 4)

• 範囲条件

>>> x = 3
>>> if 1 < x and x < 5:
...     print 'yatta!'
...     
...     
yatta!
>>> if 1 < x < 5:
...     print 'yatta!'
...     
...     
yatta!

• リスト代入とタプル代入

>>> a, b = 1, 2
>>> print a, b
1 2
>>> [a, b] = 3, 4
>>> print a, b
3 4
>>> (a, b) = 5, 6
>>> print a, b
5 6
>>> (a, b) = (7, 8)
>>> print a, b
7 8
>>> [a, b] = [9, 10]
>>> print a, b       
9 10
>>> (a, b) = [11, 12]
>>> print a, b
11 12
>>> [a, b] = (13, 14)
>>> print a, b
13 14

• キーワード引数

>>> def hoge(value, type=2, status=3):
...     print value, type, status
... 
>>> hoge(1)
1 2 3
>>> hoge(4, 5)
4 5 3
>>> hoge(4, 5, 6)
4 5 6
>>> 
>>> hoge(1, status=2)
1 2 2
>>> hoge(1, status=7)
1 2 7
>>> hoge(1, type=7, status=8)
1 7 8
>>> hoge(1, status=9, type=10)
1 10 9    

• 複数の引数

>>> def fuga(*args, **kwargs):
...     print args, kwargs
...     
>>> fuga(1)
(1,) {}
>>> fuga(1,2)
(1, 2) {}
>>> fuga(1,2,value=3)
(1, 2) {'value': 3}
>>> fuga(1,2,value=3,type=4)
(1, 2) {'type': 4, 'value': 3}

• リスト内包表記

>>> [x for x in range(1,10) if x % 2]
[1, 3, 5, 7, 9]
>>> [x * 2 for x in range(1,10)]
[2, 4, 6, 8, 10, 12, 14, 16, 18]

• lambda式（無名関数）

>>> def func1(x):
...     return x * 2
... 
>>> for x in range(1,5):
...     print func1(x)
...     
...     
2
4
6
8
10
>>> func2 = lambda x : x * 2
>>> for x in range(1,5):
...     print func2(x)
...     
...     
2
4
6
8
10

• ジェネレータ

>>> def hoge(list):
...     for i in list:
...         yield i
...         
...         
>>> fuga = hoge(range(5))
>>> fuga.next()
0
>>> fuga.next()
1
>>> fuga.next()
2
>>> fuga.next()
3
>>> fuga.next()
4
>>> fuga.next()
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
StopIteration

• デコレータ

>>> def p(*args, **kwargs):
...     print args, kwargs
...     
>>> p(1, hoge=2)
(1,) {'hoge': 2}
>>> def add_line(func):
...     def wrapper(*args, **kwargs):
...         print '----------------'
...         func(*args, **kwargs)
...         print '----------------'
...     wrapper.__name__ = func.__name__
...     return wrapper
... 
>>> @add_line
... def p(*args, **kwargs):
...     print args, kwargs
...     
>>> p(1, hoge=2)
----------------
(1,) {'hoge': 2}
----------------