for (i=0; i<list.length; i++) {
    n = list[i];
}

>>> d = {'a': 1, 'b': 2, 'c': 3}
>>> for key in d:
...     print(key)
...
a
c
b

>>> for ch in 'ABC':
...     print(ch)
...
A
B
C

>>> from collections import Iterable
>>> isinstance('abc', Iterable) # str是否可迭代
True
>>> isinstance([1,2,3], Iterable) # list是否可迭代
True
>>> isinstance(123, Iterable) # 整数是否可迭代
False

>>> for i, value in enumerate(['A', 'B', 'C']):
...     print(i, value)
...
0 A
1 B
2 C
#对比：
for i in enumerate(['A', 'B', 'C']):
    print(i)

>>> for x, y in [(1, 1), (2, 4), (3, 9)]:
...     print(x, y)
...
1 1
2 4
3 9

>>> list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> L = []
>>> for x in range(1, 11):
...    L.append(x * x)
...
>>> L
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

>>> [x * x for x in range(1, 11)]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

>>> [x * x for x in range(1, 11) if x % 2 == 0]
[4, 16, 36, 64, 100]

>>> [m + n for m in 'ABC' for n in 'XYZ']
['AX', 'AY', 'AZ', 'BX', 'BY', 'BZ', 'CX', 'CY', 'CZ']

>>> import os # 导入os模块，模块的概念后面讲到
>>> [d for d in os.listdir('.')] # os.listdir可以列出文件和目录
['.emacs.d', '.ssh', '.Trash', 'Adlm', 'Applications', 'Desktop', 'Documents', 'Downloads', 'Library', 'Movies', 'Music', 'Pictures', 'Public', 'VirtualBox VMs', 'Workspace', 'XCode']

>>> d = {'x': 'A', 'y': 'B', 'z': 'C' }
>>> for k, v in d.items():
...     print(k, '=', v)
...
y = B
x = A
z = C

>>> d = {'x': 'A', 'y': 'B', 'z': 'C' }
>>> [k + '=' + v for k, v in d.items()]
['y=B', 'x=A', 'z=C']

>>> L = ['Hello', 'World', 'IBM', 'Apple']
>>> [s.lower() for s in L]
['hello', 'world', 'ibm', 'apple']

>>> L = ['Hello', 'World', 18, 'Apple', None]
>>> [s.lower() for s in L]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
AttributeError: 'int' object has no attribute 'lower'

>>> x = 'abc'
>>> y = 123
>>> isinstance(x, str)
True
>>> isinstance(y, str)
False

# -*- coding: utf-8 -*-
L1 = ['Hello', 'World', 18, 'Apple', None]
L2 = [ s.lower() for s in L1 if isinstance(s, str)]
print(L2)

>>> L = ['Michael', 'Sarah', 'Tracy', 'Bob', 'Jack']

>>> [L[0], L[1], L[2]]
['Michael', 'Sarah', 'Tracy']

>>> r = []
>>> n = 3
>>> for i in range(n):
...     r.append(L[i])
... 
>>> r
['Michael', 'Sarah', 'Tracy']

>>> L[0:3]
['Michael', 'Sarah', 'Tracy']

>>> L[:3]
['Michael', 'Sarah', 'Tracy']

>>> L[1:3]
['Sarah', 'Tracy']

>>> L[-2:]
['Bob', 'Jack']
>>> L[-2:-1]
['Bob']

>>> L = list(range(100))
>>> L
[0, 1, 2, 3, ..., 99]

>>> L[:10]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> L[-10:]
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

>>> L[10:20]
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

>>> L[:10:2]
[0, 2, 4, 6, 8]

>>> L[::5]
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]

>>> L[:]
[0, 1, 2, 3, ..., 99]

>>> (0, 1, 2, 3, 4, 5)[:3]
(0, 1, 2)

>>> 'ABCDEFG'[:3]
'ABC'
>>> 'ABCDEFG'[::2]
'ACEG'

>>> 'ABCDEFG'[::-1]
'GFEDCBA'

# -*- coding: utf-8 -*-
def trim(s):
    return s

def trim(s):
    if s == '' :
        return ''
    elif s[0] == ' ' :
        return trim(s[1:])
    elif s[-1] == ' ' :
        return trim(s[:-1])
    else :
        return s

def power(x):
    return x * x

>>> power(5)
25
>>> power(15)
225

def power(x, n):
    s = 1
    while n > 0:
        n = n - 1
        s = s * x
    return s

>>> power(5, 2)
25
>>> power(5, 3)
125

>>> power(5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: power() missing 1 required positional argument: 'n'

def power(x, n=2):
    s = 1
    while n > 0:
        n = n - 1
        s = s * x
    return s

>>> power(5)
25
>>> power(5, 2)
25

def enroll(name, gender):
    print('name:', name)
    print('gender:', gender)

>>> enroll('Sarah', 'F')
name: Sarah
gender: F

def enroll(name, gender, age=6, city='Beijing'):
    print('name:', name)
    print('gender:', gender)
    print('age:', age)
    print('city:', city)

>>> enroll('Sarah', 'F')
name: Sarah
gender: F
age: 6
city: Beijing

enroll('Bob', 'M', 7)
enroll('Adam', 'M', city='Tianjin')

def add_end(L=[]):
    L.append('END')
    return L

>>> add_end([1, 2, 3])
[1, 2, 3, 'END']
>>> add_end(['x', 'y', 'z'])
['x', 'y', 'z', 'END']

>>> add_end()
['END']

>>> add_end()
['END', 'END']
>>> add_end()
['END', 'END', 'END']

def add_end(L=None):
    if L is None:
        L = []
    L.append('END')
    return L

>>> add_end()
['END']
>>> add_end()
['END']

def calc(numbers):
    sum = 0
    for n in numbers:
        sum = sum + n * n
    return sum

>>> calc([1, 2, 3])
14
>>> calc((1, 3, 5, 7))
84

>>> calc(1, 2, 3)
14
>>> calc(1, 3, 5, 7)
84

def calc(*numbers):
    sum = 0
    for n in numbers:
        sum = sum + n * n
    return sum

>>> calc(1, 2)
5
>>> calc()
0

>>> nums = [1, 2, 3]
>>> calc(nums[0], nums[1], nums[2])
14

>>> nums = [1, 2, 3]
>>> calc(*nums)
14

def person(name, age, **kw):
    print('name:', name, 'age:', age, 'other:', kw)

>>> person('Michael', 30)
name: Michael age: 30 other: {}

>>> person('Bob', 35, city='Beijing')
name: Bob age: 35 other: {'city': 'Beijing'}
>>> person('Adam', 45, gender='M', job='Engineer')
name: Adam age: 45 other: {'gender': 'M', 'job': 'Engineer'}

>>> extra = {'city': 'Beijing', 'job': 'Engineer'}
>>> person('Jack', 24, city=extra['city'], job=extra['job'])
name: Jack age: 24 other: {'city': 'Beijing', 'job': 'Engineer'}

>>> extra = {'city': 'Beijing', 'job': 'Engineer'}
>>> person('Jack', 24, **extra)
name: Jack age: 24 other: {'city': 'Beijing', 'job': 'Engineer'}

def person(name, age, **kw):
    if 'city' in kw:
        # 有city参数
        pass
    if 'job' in kw:
        # 有job参数
        pass
    print('name:', name, 'age:', age, 'other:', kw)

>>> person('Jack', 24, city='Beijing', addr='Chaoyang', zipcode=123456)

def person(name, age, *, city, job):
    print(name, age, city, job)

>>> person('Jack', 24, city='Beijing', job='Engineer')
Jack 24 Beijing Engineer

def person(name, age, *args, city, job):
    print(name, age, args, city, job)

>>> person('Jack', 24, 'Beijing', 'Engineer')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: person() takes 2 positional arguments but 4 were given

def person(name, age, *, city='Beijing', job):
    print(name, age, city, job)

>>> person('Jack', 24, job='Engineer')
Jack 24 Beijing Engineer

def person(name, age, city, job):
    # 缺少 *，city和job被视为位置参数
    pass

def f1(a, b, c=0, *args, **kw):
    print('a =', a, 'b =', b, 'c =', c, 'args =', args, 'kw =', kw)

def f2(a, b, c=0, *, d, **kw):
    print('a =', a, 'b =', b, 'c =', c, 'd =', d, 'kw =', kw)

>>> f1(1, 2)
a = 1 b = 2 c = 0 args = () kw = {}
>>> f1(1, 2, c=3)
a = 1 b = 2 c = 3 args = () kw = {}
>>> f1(1, 2, 3, 'a', 'b')
a = 1 b = 2 c = 3 args = ('a', 'b') kw = {}
>>> f1(1, 2, 3, 'a', 'b', x=99)
a = 1 b = 2 c = 3 args = ('a', 'b') kw = {'x': 99}
>>> f2(1, 2, d=99, ext=None)
a = 1 b = 2 c = 0 d = 99 kw = {'ext': None}

>>> args = (1, 2, 3, 4)
>>> kw = {'d': 99, 'x': '#'}
>>> f1(*args, **kw)
a = 1 b = 2 c = 3 args = (4,) kw = {'d': 99, 'x': '#'}
>>> args = (1, 2, 3)
>>> kw = {'d': 88, 'x': '#'}
>>> f2(*args, **kw)
a = 1 b = 2 c = 3 d = 88 kw = {'x': '#'}

# -*- coding: utf-8 -*-
def product(x, y):
    return x * y

def product(x, *arge):
	for i in arge:
		x = x * i 
	return x
def product_new(*num):
    if num is None or len(num) < 1 :
        raise TypeError("args not null！")
    else :
        sum = 1
        for i in num :
            sum = sum * i
        return sum 
# 测试
if __name__ == '__main__':
    print('product(5) =', product(5))
    print('product(5, 6) =', product(5, 6))
    print('product(5, 6, 7) =', product(5, 6, 7))
    print('product(5, 6, 7, 9) =', product(5, 6, 7, 9))
    if product(5) != 5:
        print('测试失败!')
    elif product(5, 6) != 30:
        print('测试失败!')
    elif product(5, 6, 7) != 210:
        print('测试失败!')
    elif product(5, 6, 7, 9) != 1890:
        print('测试失败!')
    else:
        try:
            product()
            print('测试失败!')
        except TypeError:
            print('测试成功!')

>>> abs(100)
100
>>> abs(-20)
20
>>> abs(12.34)
12.34

>>> abs(1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: abs() takes exactly one argument (2 given)

>>> abs('a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bad operand type for abs(): 'str'

>>> max(1, 2)
2
>>> max(2, 3, 1, -5)
3

>>> int('123')
123
>>> int(12.34)
12
>>> float('12.34')
12.34
>>> str(1.23)
'1.23'
>>> str(100)
'100'
>>> bool(1)
True
>>> bool('')
False
>>> hex(255)
'0xff'

>>> a = abs # 变量a指向abs函数
>>> a(-1) # 所以也可以通过a调用abs函数
1

┌────────────────────────────────────────────────────────┐
│Command Prompt - python                           - □ x │
├────────────────────────────────────────────────────────┤
│>>> def my_abs(x):                                      │
│...     if x >= 0:                                      │
│...         return x                                    │
│...     else:                                           │
│...         return -x                                   │
│...                                                     │
│>>> my_abs(-9)                                          │
│9                                                       │
│>>> _                                                   │
│                                                        │
│                                                        │
└────────────────────────────────────────────────────────┘

┌────────────────────────────────────────────────────────┐
│Command Prompt - python                           - □ x │
├────────────────────────────────────────────────────────┤
│>>> from abstest import my_abs                          │
│>>> my_abs(-9)                                          │
│9                                                       │
│>>> _                                                   │
│                                                        │
│                                                        │
│                                                        │
│                                                        │
│                                                        │
│                                                        │
│                                                        │
└────────────────────────────────────────────────────────┘

def nop():
    pass

if age >= 18:
    pass

>>> my_abs(1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: my_abs() takes 1 positional argument but 2 were given

>>> my_abs('A')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in my_abs
TypeError: unorderable types: str() >= int()
>>> abs('A')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bad operand type for abs(): 'str'

def my_abs(x):
    if not isinstance(x, (int, float)):
        raise TypeError('bad operand type')
    if x >= 0:
        return x
    else:
        return -x

>>> my_abs('A')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in my_abs
TypeError: bad operand type

import math

def move(x, y, step, angle=0):
    nx = x + step * math.cos(angle)
    ny = y - step * math.sin(angle)
    return nx, ny

>>> x, y = move(100, 100, 60, math.pi / 6)
>>> print(x, y)
151.96152422706632 70.0

>>> r = move(100, 100, 60, math.pi / 6)
>>> print(r)
(151.96152422706632, 70.0)

# -*- coding: utf-8 -*-

import math

def quadratic(a, b, c):
    x1 = ( -b + math.sqrt( b * b - 4 * a * c ) ) / ( 2 * a )
    x2 = ( -b - math.sqrt( b * b - 4 * a * c ) ) / ( 2 * a )
    return x1, x2
    
print('quadratic(2, 3, 1) =', quadratic(2, 3, 1))
print('quadratic(1, 3, -4) =', quadratic(1, 3, -4))

if quadratic(2, 3, 1) != (-0.5, -1.0):
    print('测试失败')
elif quadratic(1, 3, -4) != (1.0, -4.0):
    print('测试失败')
else:
    print('测试成功')

def fact(n):
    if n==1:
        return 1
    return n * fact(n - 1)

>>> fact(1)
1
>>> fact(5)
120
>>> fact(100)
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000

===> fact(5)
===> 5 * fact(4)
===> 5 * (4 * fact(3))
===> 5 * (4 * (3 * fact(2)))
===> 5 * (4 * (3 * (2 * fact(1))))
===> 5 * (4 * (3 * (2 * 1)))
===> 5 * (4 * (3 * 2))
===> 5 * (4 * 6)
===> 5 * 24
===> 120

>>> fact(1000)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in fact
  ...
  File "<stdin>", line 4, in fact
RuntimeError: maximum recursion depth exceeded in comparison

def fact(n):
    return fact_iter(n, 1)

def fact_iter(num, product):
    if num == 1:
        return product
    return fact_iter(num - 1, num * product)

===> fact_iter(5, 1)
===> fact_iter(4, 5)
===> fact_iter(3, 20)
===> fact_iter(2, 60)
===> fact_iter(1, 120)
===> 120

# -*- coding: utf-8 -*-
def move(n, a, b, c):
    if n == 1:
        print(a, '-->', c)
    else:
        move(n-1, a, c, b)
        move(1, a, b, c)
        move(n-1, b, a, c)

sudo yum remove docker \
                  docker-client \
                  docker-client-latest \
                  docker-common \
                  docker-latest \
                  docker-latest-logrotate \
                  docker-logrotate \
                  docker-selinux \
                  docker-engine-selinux \
                  docker-engine

sudo yum install -y yum-utils \
  device-mapper-persistent-data \
  lvm2

sudo yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo

sudo yum install docker-ce
sudo usermod -aG docker your-user #普通用户要使用docker需要添加到docker组

sudo systemctl start docker
docker  version #查看版本

sudo yum install /path/to/package.rpm
sudo usermod -aG docker your-user #普通用户要使用docker需要添加到docker组
sudo systemctl start docker
docker  version #查看版本

curl -fsSL get.docker.com -o get-docker.sh
sudo sh get-docker.sh
sudo usermod -aG docker your-user #普通用户要使用docker需要添加到docker组
sudo systemctl start docker
docker  version #查看版本

names = ['Michael', 'Bob', 'Tracy']
scores = [95, 75, 85]

>>> d = {'Michael': 95, 'Bob': 75, 'Tracy': 85}
>>> d['Michael']
95

>>> d['Adam'] = 67
>>> d['Adam']
67

>>> d['Jack'] = 90
>>> d['Jack']
90
>>> d['Jack'] = 88
>>> d['Jack']
88

>>> d['Thomas']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'Thomas'

>>> 'Thomas' in d
False

>>> d.get('Thomas')
>>> d.get('Thomas', -1)
-1

>>> d.pop('Bob')
75
>>> d
{'Michael': 95, 'Tracy': 85}

>>> key = [1, 2, 3]
>>> d[key] = 'a list'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

>>> s = set([1, 2, 3])
>>> s
{1, 2, 3}

>>> s = set([1, 1, 2, 2, 3, 3])
>>> s
{1, 2, 3}

>>> s.add(4)
>>> s
{1, 2, 3, 4}
>>> s.add(4)
>>> s
{1, 2, 3, 4}

>>> s.remove(4)
>>> s
{1, 2, 3}

>>> s1 = set([1, 2, 3])
>>> s2 = set([2, 3, 4])
>>> s1 & s2
{2, 3}
>>> s1 | s2
{1, 2, 3, 4}

>>> a = ['c', 'b', 'a']
>>> a.sort()
>>> a
['a', 'b', 'c']

>>> a = 'abc'
>>> a.replace('a', 'A')
'Abc'
>>> a
'abc'

>>> a = 'abc'
>>> b = a.replace('a', 'A')
>>> b
'Abc'
>>> a
'abc'

┌───┐                  ┌───────┐
│ a │─────────────────>│ 'abc' │
└───┘                  └───────┘

┌───┐                  ┌───────┐
│ a │─────────────────>│ 'abc' │
└───┘                  └───────┘
┌───┐                  ┌───────┐
│ b │─────────────────>│ 'Abc' │
└───┘                  └───────┘

age = 20
if age >= 18:
    print('your age is', age)
    print('adult')

age = 3
if age >= 18:
    print('your age is', age)
    print('adult')
else:
    print('your age is', age)
    print('teenager')

age = 3
if age >= 18:
    print('adult')
elif age >= 6:
    print('teenager')
else:
    print('kid')

if <条件判断1>:
    <执行1>
elif <条件判断2>:
    <执行2>
elif <条件判断3>:
    <执行3>
else:
    <执行4>

age = 20
if age >= 6:
    print('teenager')
elif age >= 18:
    print('adult')
else:
    print('kid')

if x:
    print('True')

birth = input('birth: ')
if birth < 2000:
    print('00前')
else:
    print('00后')
#这个我在jupyter notebook 上面测试没有问题
#但是在Python 代码行中就如上面所说

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unorderable types: str() > int()

s = input('birth: ')
birth = int(s)
if birth < 2000:
    print('00前')
else:
    print('00后')

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'abc'

>>> 1 + 2 + 3
6

names = ['Michael', 'Bob', 'Tracy']
for name in names:
    print(name)

Michael
Bob
Tracy

sum = 0
for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:
    sum = sum + x
print(sum)

>>> list(range(5))
[0, 1, 2, 3, 4]

# -*- coding: utf-8 -*-
sum = 0
for x in range(101):
    sum = sum + x
print(sum)

sum = 0
n = 99
while n > 0:
    sum = sum + n
    n = n - 2
print(sum)

while y != 0 or x != 0 :  #这个是while 中加两个判断，然后or，也可以and 或者not

n = 1
while n <= 100:
    print(n)
    n = n + 1
print('END')

n = 1
while n <= 100:
    if n > 10: # 当n = 11时，条件满足，执行break语句
        break # break语句会结束当前循环
    print(n)
    n = n + 1
print('END')

n = 0
while n < 10:
    n = n + 1
    print(n)

n = 0
while n < 10:
    n = n + 1
    if n % 2 == 0: # 如果n是偶数，执行continue语句
        continue # continue语句会直接继续下一轮循环，后续的print()语句不会执行
    print(n)

>>> classmates = ['Michael', 'Bob', 'Tracy']
>>> classmates
['Michael', 'Bob', 'Tracy']

>>> len(classmates)
3

>>> classmates[0]
'Michael'
>>> classmates[1]
'Bob'
>>> classmates[2]
'Tracy'
>>> classmates[3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

>>> classmates[-1]
'Tracy'

>>> classmates[-2]
'Bob'
>>> classmates[-3]
'Michael'
>>> classmates[-4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

>>> classmates.append('Adam')
>>> classmates
['Michael', 'Bob', 'Tracy', 'Adam']

>>> classmates.insert(1, 'Jack')
>>> classmates
['Michael', 'Jack', 'Bob', 'Tracy', 'Adam']

>>> classmates.pop()
'Adam'
>>> classmates
['Michael', 'Jack', 'Bob', 'Tracy']

>>> classmates.pop(1)
'Jack'
>>> classmates
['Michael', 'Bob', 'Tracy']

>>> classmates[1] = 'Sarah'
>>> classmates
['Michael', 'Sarah', 'Tracy']

>>> L = ['Apple', 123, True]

>>> s = ['python', 'java', ['asp', 'php'], 'scheme']
>>> len(s)
4

>>> p = ['asp', 'php']
>>> s = ['python', 'java', p, 'scheme']

>>> L = []
>>> len(L)
0

>>> classmates = ('Michael', 'Bob', 'Tracy')

>>> t = (1, 2)
>>> t
(1, 2)

>>> t = ()
>>> t
()

>>> t = (1)
#等同于 t = 1
>>> t
1

>>> t = (1,)
>>> t
(1,)

>>> t = ('a', 'b', ['A', 'B'])
>>> t[2][0] = 'X'
>>> t[2][1] = 'Y'
>>> t
('a', 'b', ['X', 'Y'])

>>> print('包含中文的str')
包含中文的str

>>> ord('A')
65
>>> chr(66)
'B'
#注意下面两个在jupyter notebook中会报错，但是在python命令行中却不会错, 看看你的locale charmap是否为utf-8
>>> ord('中')
20013
>>> chr(25991)
'文'

>>> 'ABC'.encode('ascii')
b'ABC'
>>> '中文'.encode('utf-8')
b'\xe4\xb8\xad\xe6\x96\x87'
>>> '中文'.encode('ascii')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128)

>>> b'ABC'.decode('ascii')
'ABC'
>>> b'\xe4\xb8\xad\xe6\x96\x87'.decode('utf-8')
'中文'

>>> b'\xe4\xb8\xad\xff'.decode('utf-8')
Traceback (most recent call last):
  ...
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 3: invalid start byte

>>> b'\xe4\xb8\xad\xff'.decode('utf-8', errors='ignore')
'中'

>>> len('ABC')
3
>>> len('中文')
2

>>> len(b'ABC')
3
>>> len(b'\xe4\xb8\xad\xe6\x96\x87')
6
>>> len('中文'.encode('utf-8'))
6

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

>>> 'Hello, %s' % 'world'
'Hello, world'
>>> 'Hi, %s, you have $%d.' % ('Michael', 1000000)
'Hi, Michael, you have $1000000.'

# -*- coding: utf-8 -*-
print('%2d-%02d' % (3, 1))
print('%.2f' % 3.1415926)

>>> 'Age: %s. Gender: %s' % (25, True)
'Age: 25. Gender: True'

>>> 'growth rate: %d %%' % 7
'growth rate: 7 %'

>>> 'Hello, {0}, 成绩提升了 {1:.1f}%'.format('小明', 17.125)
'Hello, 小明, 成绩提升了 17.1%'

>>> '中文'.encode('gb2312')
b'\xd6\xd0\xce\xc4'