作者 | 许向武
责编 | 郭芮
出品 | CSDN 博客
for - else
>>> for i in [1,2,3,4]:
print(i)
else:
print(i, '我是else')
1
2
3
4
4 我是else
>>> for i in [1,2,3,4]:
if i > 2:
print(i)
else:
print(i, '我是else')
3
4
4 我是else
>>> for i in [1,2,3,4]:
if i>2:
print(i)
break
else:
print(i, '我是else')
3
一颗星()和两颗星(*)
>>> def multi_sum(*args):
s = 0
for item in args:
s += item
return s
>>> multi_sum(3,4,5)
12
>>> def do_something(name, age, gender='男', *args, **kwds):
print('姓名：%s，年龄：%d，性别：%s'%(name, age, gender))
print(args)
print(kwds)
>>> do_something('xufive', 50, '男', 175, 75, math=99, english=90)
姓名：xufive，年龄：50，性别：男
(175, 75)
{'math': 99, 'english': 90}
三元表达式
>>> y = 5
>>> if y < 0:
print('y是一个负数')
else:
print('y是一个非负数')
y是一个非负数
打球去吧 if 不下雨 else 去自习室
>>> y = 5
>>> print('y是一个负数' if y < 0 else 'y是一个非负数')
y是一个非负数
>>> y = 5
>>> x = -1 if y < 0 else 1
>>> x
1
with - as
fp = open(r"D:\CSDN\Column\temp\mpmap.py", 'r')
try:
contents = fp.readlines()
finally:
fp.close()
>>> with open(r"D:\CSDN\Column\temp\mpmap.py", 'r') as fp:
contents = fp.readlines()
列表推导式
>>> a = [1, 2, 3, 4, 5]
>>> result = list()
>>> for i in a:
result.append(i*i)
>>> result
[1, 4, 9, 16, 25]
>>> a = [1, 2, 3, 4, 5]
>>> result = [i*i for i in a]
>>> result
[1, 4, 9, 16, 25]
列表索引的各种骚操作
>>> a = [0, 1, 2, 3, 4, 5]
>>> a[2:4]
[2, 3]
>>> a[3:]
[3, 4, 5]
>>> a[1:]
[1, 2, 3, 4, 5]
>>> a[:]
[0, 1, 2, 3, 4, 5]
>>> a[::2]
[0, 2, 4]
>>> a[1::2]
[1, 3, 5]
>>> a[-1]
5
>>> a[-2]
4
>>> a[1:-1]
[1, 2, 3, 4]
>>> a[::-1]
[5, 4, 3, 2, 1, 0]
>>> a = [0, 1, 2, 3, 4, 5]
>>> b = ['a', 'b']
>>> a[2:2] = b
>>> a
[0, 1, 'a', 'b', 2, 3, 4, 5]
>>> a[3:6] = b
>>> a
[0, 1, 'a', 'a', 'b', 4, 5]
lambda函数
>>> lambda x,y: x+y
<function <lambda> at 0x000001B2DE5BD598>
>>> (lambda x,y: x+y)(3,4) # 因为匿名函数没有名字，使用的时候要用括号把它包起来
>>> a = [{'name':'B', 'age':50}, {'name':'A', 'age':30}, {'name':'C', 'age':40}]
>>> sorted(a, key=lambda x:x['name']) # 按姓名排序
[{'name': 'A', 'age': 30}, {'name': 'B', 'age': 50}, {'name': 'C', 'age': 40}]
>>> sorted(a, key=lambda x:x['age']) # 按年龄排序
[{'name': 'A', 'age': 30}, {'name': 'C', 'age': 40}, {'name': 'B', 'age': 50}]
>>> a = [1,2,3]
>>> for item in map(lambda x:x*x, a):
print(item, end=', ')
1, 4, 9,
yield 以及生成器和迭代器
>>> a = [1,2,3]
>>> a_iter = iter(a)
>>> a_iter
<list_iterator object at 0x000001B2DE434BA8>
>>> for i in a_iter:
print(i, end=', ')
1, 2, 3,
>>> def get_square(n):
result = list()
for i in range(n):
result.append(pow(i,2))
return result
>>> print(get_square(5))
[0, 1, 4, 9, 16]
>>> def get_square(n):
for i in range(n):
yield(pow(i,2))
>>> a = get_square(5)
>>> a
<generator object get_square at 0x000001B2DE5CACF0>
>>> for i in a:
print(i, end=', ')
0, 1, 4, 9, 16,
装饰器
>>> import time
>>> def timer(func):
def wrapper(*args,**kwds):
t0 = time.time()
func(*args,**kwds)
t1 = time.time()
print('耗时%0.3f'%(t1-t0,))
return wrapper
>>> @timer
def do_something(delay):
print('函数do_something开始')
time.sleep(delay)
print('函数do_something结束')
>>> do_something(3)
函数do_something开始
函数do_something结束
耗时3.077
巧用断言assert
>>> def i_want_to_sleep(delay):
assert(isinstance(delay, (int,float))), '函数参数必须为整数或浮点数'
print('开始睡觉')
time.sleep(delay)
print('睡醒了')
>>> i_want_to_sleep(1.1)
开始睡觉
睡醒了
>>> i_want_to_sleep(2)
开始睡觉
睡醒了
>>> i_want_to_sleep('2')
Traceback (most recent call last):
File "<pyshell#247>", line 1, in <module>
i_want_to_sleep('2')
File "<pyshell#244>", line 2, in i_want_to_sleep
assert(isinstance(delay, (int,float))), '函数参数必须为整数或浮点数'
AssertionError: 函数参数必须为整数或浮点数
【End】
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