python手記（11）------並行迭代+列表解析

1.zip()

In[30]: a
Out[28]: 
[1, 2, 3, 4, 5]
In[31]: b
Out[29]: 
[3, 4, 5, 6, 7]
In[32]: a[i]+b[i]   ————————————解決該問題方法一

In[27]: c=[]
In[28]: for i in range(5):
...     c.append(a[i]+b[i])
...     
In[29]: c
Out[27]: 
[4, 6, 8, 10, 12]

 　　另一個方法則為並行迭代，需要zip()函式：zip(迭代物件1，迭代物件2，迭代物件3……)--------》返回一個zip物件

 

In[33]: help(zip)
Help on class zip in module builtins:

class zip(object)
 |  zip(iter1 [,iter2 [...]]) --> zip object
 |  
 |  Return a zip object whose .__next__() method returns a tuple where
 |  the i-th element comes from the i-th iterable argument.  The .__next__()
 |  method continues until the shortest iterable in the argument sequence
 |  is exhausted and then it raises StopIteration.

 

In[49]: a='abcde'
In[50]: b='12345'
In[51]: tuple(zip(a,b))
Out[48]: 
(('a', '1'), ('b', '2'), ('c', '3'), ('d', '4'), ('e', '5'))
In[52]: list(zip(a,b))
Out[49]: 
[('a', '1'), ('b', '2'), ('c', '3'), ('d', '4'), ('e', '5')]

　　解決a+b問題：

In[73]: a
Out[70]: 
[1, 2, 3, 4, 5]
In[74]: b
Out[71]: 
[3, 4, 5, 6, 7]
In[75]: c=[]
In[76]: for i,j in zip(a,b):
...     c.append(i+j)
...     
In[77]: c
Out[74]: 
[4, 6, 8, 10, 12]

 

2.enumerate()函式，同時得到索引和值：enumerate(可迭代物件，[開始計數值])-------->（（索引1，值），（索引2，值）……）

In[83]: a='abcdefghijklmn'
In[84]: b=list(enumerate(a))
In[85]: b
Out[82]:        #索引和值的混合輸出結果

[(0, 'a'),
 (1, 'b'),
 (2, 'c'),
 (3, 'd'),
 (4, 'e'),
 (5, 'f'),
 (6, 'g'),
 (7, 'h'),
 (8, 'i'),
 (9, 'j'),
 (10, 'k'),
 (11, 'l'),
 (12, 'm'),
 (13, 'n')]

　　

 In[86]: b=list(enumerate(a,start=1))
 In[87]: b
 Out[84]:

 [(1, 'a'),
 (2, 'b'),
 (3, 'c'),
 (4, 'd'),
 (5, 'e'),
 (6, 'f'),
 (7, 'g'),
 (8, 'h'),
 (9, 'i'),
 (10, 'j'),
 (11, 'k'),
 (12, 'l'),
 (13, 'm'),
 (14, 'n')]

　　

 

3.列表解析：[表示式（i）for i in（可迭代物件）]

In[92]: list(range(0,100,5))
Out[89]: 
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]
In[93]: i=1
In[94]: [i for i in range(0,100,5)]    #100以內5的整數倍
Out[91]: 
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]

In[96]: [i**0.5 for i in range(10)]    #10以內，每個數的平方根
Out[93]: 

[0.0,
 1.0,
 1.4142135623730951,
 1.7320508075688772,
 2.0,
 2.23606797749979,
 2.449489742783178,
 2.6457513110645907,
 2.8284271247461903,
 3.0]