Python语句

赋值语句

>>> (x,y) = (5,10)

>>> x

5

>>> y

10

>>> x,y = 5,10

>>> x,y

(5, 10)

>>> [x,y,z] = [1,2,3]

>>> x,y,z

(1, 2, 3)

>>> x,y = y,x

>>> x,y

(2, 1)

>>> [a,b,c] = (1,2,3)

#序列赋值

>>> a,b,c = 'abc'

>>> a

'a'

>>> b

'b'

>>> c

'c'

#左右两边不一致

>>> a,b,*c = 'abcdefgh'

>>> a

'a'

>>> b

'b'

>>> c

['c', 'd', 'e', 'f', 'g', 'h']

>>> a,*b,c = 'abcdefgh'

>>> a

'a'

>>> b

['b', 'c', 'd', 'e', 'f', 'g']

>>> c

'h'

>>> s = 'abcderf'

>>> a,b,c = s[0],s[1],s[2:]

>>> a

'a'

>>> b

'b'

>>> c

'cderf

>>> a,b,c,*d = 'abc'

>>> a

'a'

>>> b

'b'

>>> c

'c'

>>> d

[]

>>> a = b = c = 'hello'

>>> a

'hello'

>>> b

'hello'

>>> a = 'hello'

>>> b = 'world'

>>> print(a,b)

hello world

>>> print(a,b,sep='|')

hello|world

>>> print(a,b,sep='|',end='...\n')

hello|world...

>>> print(a,b,end='...\n',file=open('result.txt','w'))

条件语句

score = 75

if score >= 90:

print('优秀')

elif score >= 80:

print('良好')

elif score >= 60:

print('及格')

else:

print('不及格')

def add(x):

print(x + 10)

operation = {

'add': add,

'update': lambda x: print(x * 2),

'delete': lambda x: print(x * 3)

}

operation.get('add')(10)

operation.get('update')(10)

operation.get('delete')(10)

#三元表达式

result = '及格' if score >= 60 else '不及格'

循环语句

while循环

x = 'hello world'

while x:

print(x,end='|')

x = x[1:]

#hello world|ello world|llo world|lo world|o world| world|world|orld|rld|ld|d|

#continue

x = 10

while x:

x -= 1

if(x % 2 != 0):

continue

print(x)

#break、else

while True:

name = input('请输入姓名：')

if name == 'stop':

break

age = input('请输入年龄：')

print('{}---{}'.format(name,age))

else:

print('循环结束')

#else

for循环

for x in [1,2,3,4]:

print(x, end='|')

for key in emp:

print(key)

for k,v in emp.items():

print(k,v)

s1 = 'abcd'

s2 = 'cdef'

result = []

for x in s1:

if x in s2:

result.append(x)

result = [x for x in s1 if x in s2]

for x in range(1,100):

print(x)

for x in range(1,101,2):

print(x)

for index,item in enumerate(s1):

print(index,item)

迭代

迭代协议：__ next__()

全局函数：next()

f = open('a.txt',encoding='utf8')

for line in f:

print(line)

可迭代的对象分为两类：

? 迭代器对象：已经实现(文件)

? 可迭代对象：需要iter()-->__ iter__方法生成迭代器(列表)

f = open('a.txt')

iter(f) is f

True

l = [1,2,3]

iter(l) is l

False

l = iter(l)

l.__next__()

1

l = [1,2,3]

res = [x + 10 for x in l ]

res

[11, 12, 13]

res = [x for x in l if x >= 2]

res

[2, 3]

result = zip(['x','y','z'],[1,2,3])

result

for x in result:

print(x)

('x', 1)

('y', 2)

('z', 3)

Python之函数

函数的作用域：

Local

Global

Built-in

Enclousure(nolocal)

x = 100

def func():

x = 0

print(x)

print('全局x：', x)

func()

全局x： 100

0

------------------------------------------

x = 100

def func():

global x

x = 0

print(x)

print('全局x：', x)

func()

print('全局x：', x)

全局x： 100

0

全局x： 0

def func():

x = 100

def nested():

x = 99

print(x)

nested()

print(x)

func()

99

100

--------------------------------------------------------------

def func():

x = 100

def nested():

nonlocal x

x = 99

print(x)

nested()

print(x)

func()

99

99

参数

不可变类型：传递副本给参数

可变类型：传递地址引用

def fun(x):

x += 10

x = 100

print(x)

fun(x)

print(x)

100

100

---------------------------

def func(l):

l[0] = 'aaa'

l = [1,2,3,4]

print(l)

func(l)

print(l)

[1, 2, 3, 4]

['aaa', 2, 3, 4]

----------------------------------------

def func(str):

str = 'aaa'

str = '124'

print(str)

func(str)

print(str)

124

124

-------------------------------------------

def func(l):

l[0] = 'aaa'

l = [1,2,3,4]

print(l)

func(l.copy())

print(l)

[1, 2, 3, 4]

[1, 2, 3, 4]

---------------------------------------------

def func(l):

l[0] = 'aaa'

l = [1,2,3,4]

print(l)

func(l[:])

print(l)

[1, 2, 3, 4]

[1, 2, 3, 4]

*args和**kwargs

def avg(score, *scores):

return score + sum(scores) / (len(scores) + 1)

print(avg(11.2,22.4,33))

scores = (11,22,3,44)

print(avg(*scores))

----------------------------------------------------------------

emp = {

'name':'Tome',

'age':20,

'job':'dev'

}

def display_employee(**employee):

print(employee)

display_employee(name='Tom',age=20)

display_employee(**emp)

lambda

f = lambda name:print(name)

f('Tom')

f2 = lambda x,y: x+y

print(f2(3,5))

f3 = lambda : print('haha')

f3()

------------------------------

def hello(action,name):

action(name)

hello(lambda name:print('hello',name),'Tom')

--------------------------------

def add_number(x):

return x+5

l = list((range(1,10)))

#map这种方式特别灵活，可以实现非诚复杂的逻辑

print(list(map(add_number,l)))

print(list(map(lambda x:x**2,l)))

def even_number(x):

return x % 2 == 0

l = list(range(1,10))

print(list(filter(even_number,l)))

print(list(filter(lambda x : x % 2 == 0,l)))