Python中的列表生成式与生成器学习教程

> [x * x for x in range(1, 11)]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

> [x * x for x in range(1, 11) if x % 2 == 0]
[4, 16, 36, 64, 100]

> [m + n for m in 'ABC' for n in 'XYZ']
['AX', 'AY', 'AZ', 'BX', 'BY', 'BZ', 'CX', 'CY', 'CZ']

> import os
> [d for d in os.listdir('.')]
['README.md', '.git', 'image', 'os', 'lib', 'sublime-imfix', 'src']

> d = {'x': 'A', 'y': 'B', 'z': 'C' }
> [k + '=' + v for k, v in d.iteritems()]
['y=B', 'x=A', 'z=C']

> L = ['Hello', 'World', 'IBM', 'Apple']
> [s.lower() for s in L]
['hello', 'world', 'ibm', 'apple']

> L = ['Hello', 'World', 'IBM', 'Apple', 12, 34]
> [s.lower() if isinstance(s,str) else s for s in L]
['hello', 'world', 'ibm', 'apple', 12, 34]

#!/usr/bin/env python3 
# -*- coding: utf-8 -*- 
 
list(range(1, 11)) 
 
# 生成1乘1，2乘2...10乘10 
L = [] 
for x in range(1, 11): 
  L.append(x * x) 
 
# 上面太麻烦，看下面 
[x * x for x in range(1, 11)] 
# [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] 
 
# 加上if，就可以筛选出仅偶数的平方 
[x * x for x in range(1, 11) if x % 2 == 0] 
# [4, 16, 36, 64, 100] 
 
# 两层循环，可以生成全排列 
[m + n for m in 'ABC' for n in 'XYZ'] 
# ['AX', 'AY', 'AZ', 'BX', 'BY', 'BZ', 'CX', 'CY', 'CZ'] 
 
# 列出当前目录下的所有文件和目录名 
import os 
[d for d in os.listdir('.')] # on.listdir可以列出文件和目录 
 
# 列表生成式也可以使用两个变量来生成list: 
d = {'x': 'A', 'y': 'B', 'z': 'C'} 
[k + '=' + v for k, v in d.items()] 
# ['x=A', 'z=C', 'y=B'] 
 
# 把一个list中所有的字符串变成小写 
L = ['Hello', 'World', 'IBM', 'Apple'] 
[s.lower() for s in L] 
# ['hello', 'world', 'ibm', 'apple'] 
 
L1 = ['Hello', 'World', 18, 'Apple', None] 
L2 = [s.lower() for s in L1 if isinstance(s, str)] 
print(L2) 
# ['hello', 'world', 'apple'] 
# isinstance函数可以判断一个变量是不是字符串 

> g = (x * x for x in range(10))
> g
<generator object <genexpr> at 0x7fe73eb85cd0>

> g.next()
0
> g.next()
1
> g.next()
4
> g.next()
9
> g.next()
16
> g.next()
25
> g.next()
36
> g.next()
49
> g.next()
64
> g.next()
81
> g.next()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
StopIteration

> g = (x * x for x in range(10))
> for n in g:
...   print n
...

def fib(max):
  n, a, b = 0, 0, 1
  while n < max:
    print b
    a, b = b, a + b
    n = n + 1

def fib(max):
  n, a, b = 0, 0, 1
  while n < max:
    yield b
    a, b = b, a + b
    n = n + 1

> fib(6)
<generator object fib at 0x7fa1c3fcdaf0>
> fib(6).next()
1

def odd():
  print 'step 1'
  yield 1
  print 'step 2'
  yield 3
  print 'step 3'
  yield 5

> o = odd()
> o.next()
step 1
1
> o.next()
step 2
3
> o.next()
step 3
5
> o.next()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
StopIteration

def odd():
  print 'step 1'
  yield 1
  print 'step 2'
  yield 2
  print 'step 3'
  yield 3

if __name__ == '__main__':
  o = odd()
  while True:
    try:
      print o.next()
    except:
      break