%%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
%%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
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']
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}
set1 = {i for i in range(10)}
print set1
set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
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]]
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]
# 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']
f = lambda x:x**2
f(2)
4
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']
def gen_test():
for i in range(3):
yield i
gen = gen_test() #此时不执行生成器
type(gen)
generator
for i in gen: # 直到迭代时才执行
print i
0
1
2