集合推导式

列表推导式



In [1]:

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









    



1000 loops, best of 3: 1.21 ms per loop



In [2]:

    
%%timeit
#列表推导式方法
result2 = [i for i in range(10000) if i%2 == 0]









    



1000 loops, best of 3: 866 µs per loop



In [3]:

    
str_lst = ['Welcome', 'to', 'Python', 'Data', 'Analysis', 'Course']
result3 = [x.upper() for x in str_lst if len(x) > 4]
print result3









    



['WELCOME', 'PYTHON', 'ANALYSIS', 'COURSE']

字典推导式



In [4]:

    
dict1 = {key : value for key, value in enumerate(reversed(range(10)))}
print dict1









    



{0: 9, 1: 8, 2: 7, 3: 6, 4: 5, 5: 4, 6: 3, 7: 2, 8: 1, 9: 0}

集合推导式



In [5]:

    
set1 = {i for i in range(10)}
print set1









    



set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

嵌套推导式



In [6]:

    
lists = [range(10), range(10, 20)]
print lists









    



[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]]



In [7]:

    
evens = [item for lst in lists for item in lst if item % 2 == 0]
print evens









    



[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

多函数模式



In [8]:

    
# 处理字符串
str_lst = ['$1.123', ' $1123.454', '$899.12312']

def remove_space(str):
    """
        remove space
    """
    str_no_space = str.replace(' ', '')
    return str_no_space

def remove_dollar(str):
    """
        remove $
    """
    if '$' in str:
        return str.replace('$', '')
    else:
        return str

def clean_str_lst(str_lst, operations):
    """
        clean string list
    """
    result = []
    for item in str_lst:
        for op in operations:
            item = op(item)
        result.append(item)
    return result

clean_operations = [remove_space, remove_dollar]
result = clean_str_lst(str_lst, clean_operations)
print result









    



['1.123', '1123.454', '899.12312']

匿名函数 lambda



In [9]:

    
f = lambda x:x**2
f(2)









    Out[9]:





4



In [10]:

    
str_lst = ['Welcome', '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









    



['to', 'Data', 'Python', 'Course', 'Welcome', 'Analysis']
['Data', 'Course', 'Welcome', 'Python', 'to', 'Analysis']

生成器 generator



In [11]:

    
def gen_test():
    for i in range(3):
        yield i
        
gen = gen_test() #此时不执行生成器
type(gen)









    Out[11]:





generator



In [12]:

    
for i in gen: # 直到迭代时才执行
    print i



In [ ]: