python推导式，匿名函数lambda，生成器

1、推导式

列表推导式，一个表达式构造一个新列表

[exp for item in collection if condition]

exp列表中的元素

In [188]: %%timeit
.....: #普通方法
.....: result1 = []
.....: for i in range(10000):
.....:     if i%2 == 0:
.....:         result1.append(i)
.....:

1000 loops, best of 3: 1.06 ms per loop

In [189]: %%timeit
.....: #列表推导式方法
.....: result2 = [i for i in range(10000) if i%2 == 0]
.....:
1000 loops, best of 3: 846 µs per loop

In [202]: str_lst = ['Welcome', 'to', 'Python', 'Data', 'Analysis', 'Course']

In [203]: result3 = [x.upper() for x in str_lst if len(x) > 4]

In [204]: result3
Out[204]: ['WELCOME', 'PYTHON', 'ANALYSIS', 'COURSE']

字典推导式

{ key_exp: value_exp for item in collection in condition}

In [192]: dict1 = {key : value for key, value in enumerate(reversed(range(10))) if key >5}

In [193]: dict1
Out[193]: {6: 3, 7: 2, 8: 1, 9: 0}

集合推导式

{exp for item in collection if condition}

In [200]: set1 = {i+1 for i in range(10) if i > 5}

In [201]: set1
Out[201]: {7, 8, 9, 10}

2、匿名函数lambda

str_lst = ['Welcome',
9f4c
'to', 'Python', 'Data', 'Analysis', 'Course']
str_lst.sort(key=lambda x:len(x)) # sort by length
print str_lst

str_lst.sort(key=lambda x:x[-1]) # sort by the last letter
print str_lst