15.Pythonic与python杂记

switcher ={
   :'sunday',
   :'monday',
   :'thuesday'
}

day =
day_name=switcher.get(day,'Unknow')
print(day_name)  # sunday

def get_sunday():
    return 'sunday'

def get_monday():
    return 'monday'

def get_thuesday():
    return 'thuesday'

def get_default():
    return 'Unknow'

switcher ={
   :get_sunday,
   :get_monday,
   :get_thuesday
}

day =
day_name=switcher.get(day,get_default)()
print(day_name)  # sunday

# 列表推到式
# 集合推到式
# map filter
# set
# dict
a = [,,,,,,,]
# b = [i*i for i in a]
b = [i** for i in a]
print(b)  # [, , , , , , , ]
c = [i** for i in a]
print(c)  # [, , , , , , , ]
d = [i** for i in a if i > ]
print(d)  # [, , ]

e =(,,,,,,,)
f = [i** for i in a if i > ]
print(f)  # [, , ]
g = {i** for i in a if i > }
print(g)  # {, , }

students = {
    '喜小乐':,
    '石敢当':,
    '张三':
}
# 字典
b = {key for key,value in students.items()}
print(b)  # {'石敢当', '喜小乐', '张三'}
b = {value for key,value in students.items()}
print(b)  # {, , }
b = {value:key for key,value in students.items()}
print(b)  # {: '喜小乐', : '石敢当', : '张三'}

# 元组
b = (key for key,value in students.items())
for x in b:
    print(x)
# 喜小乐
# 石敢当
# 张三

# None 空
# 空字符串 空的列表  False
a = ''
b = False
c =[]
print(a==None)      # False
print(b==None)      # False
print(c==None)      # False
print(a is None)    # False
print(type(None))   # <class 'NoneType'>

a = []
a =''
a = None   # 不存在
a = False  # 真假

判断为空的方式
if a:
if not a:

class Test():
    def __len__(self):
        return
        # return
        # return True

test = Test()
if test:
    print('S')  # True/
else:
    print('F')  # 

print(len(Test()))   #
print(bool(Test()))  # False

class Test():
    def __bool__(self):
        return False

    def __len__(self):
        return True

test = Test()
if test:
    print('S')
else:
    print('F')  # F