if condition_1:
    statement_block_1
elif condition_2:
    statement_block_2
else:
    statement_block_3

x = float(input('x = '))
if x > 1:
    y = 3 * x - 5
elif x >= -1:
    y = x + 2
else:
    y = 5 * x + 3
print('f(%.2f) = %.2f' % (x, y)) 
# 这里的 %.2f 是我们前面提到的格式化输出，指保留两位小数字的浮点数输出。

f(3.20) = 4.60

age = int(input("请输入你家狗狗的年龄: "))
print("")
if age <= 0:
    print("你是在逗我吧!")
elif age == 1:
    print("相当于 14 岁的人。")
elif age == 2:
    print("相当于 22 岁的人。")
elif age > 2:
    human = 22 + (age -2)*5
    print("对应人类年龄: ", human)
 
### 退出提示
input("点击 enter 键退出")

对应人类年龄:  27

''

# 请体会以下代码为什么输出是 'teenager' 而不是 'adult'
age = 20
if age >= 6:
    print('teenager')
elif age >= 18:
    print('adult')
else:
    print('kid')

teenager

# 展示一个嵌套的 if 语句的例子
chinese_score = 80
english_score = 30

if chinese_score >=60:
    if english_score >=60:
        print('语文和英语都及格了')
    else:
        print('语文及格了，但英语没及格')
else:
    print('语文和英语都没及格')

语文及格了，但英语没及格

match subject:
    case <pattern_1>:
        <action_1>
    case <pattern_2>:
        <action_2>
    case <pattern_3>:
        <action_3>
    case _: # 表示当其他 case 都无法匹配时，匹配这条。
        <action_wildcard>

# 使用 if 语句对学生成绩进行等级匹配
score = 'B'
if score == 'A':
    print('score is A.')
elif score == 'B':
    print('score is B.')
elif score == 'C':
    print('score is C.')
else:
    print('invalid score.')

score is B.

# 改用 match 语句
score = 'B'

match score:
    case 'A':
        print('score is A.')
    case 'B':
        print('score is B.')
    case 'C':
        print('score is C.')
    case _: # _表示匹配到其他任何情况
        print('score is ???.')

score is B.

age = 15

match age:
    case x if x < 10:
        print(f'< 10 years old: {x}')
    case 10:
        print('10 years old.')
    case 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18:
        print('11~18 years old.')
    case 19:
        print('19 years old.')
    case _:
        print('not sure.')

11~18 years old.

while condition:
    statement...

# 计算 1 + 2 + ... + 100
n = 100
sum = 0
i = 1
while i <= n:
    sum = sum + i
    i += 1

print("1 到 %d 之和为: %d" % (n,sum))

1 到 100 之和为: 5050

# 这是一个死循环
while True:  # 表达式永远为 true
    print('Hello')

# 猜数字：系统随机生成一个1~100之间的整数，用户去猜一直到猜中为止。
import random

answer = random.randint(1, 100)
counter = 0
while True:
    counter += 1
    number = int(input('请输入: '))
    if number < answer:
        print('你猜的数是 %d, 大一点'% number)
    elif number > answer:
        print('你猜的数是 %d, 小一点'% number)
    else:
        print('你猜的数是 %d, 恭喜你猜对了!'% number)
        break
print('你总共猜了%d次' % counter)
if counter > 7:
    print('你的智商余额明显不足')

你猜的数是 50, 小一点
你猜的数是 30, 大一点
你猜的数是 40, 小一点
你猜的数是 35, 小一点
你猜的数是 33, 小一点
你猜的数是 31, 大一点
你猜的数是 32, 恭喜你猜对了!
你总共猜了7次

# 只打印奇数
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)

# 询问用户名及密码
while True:
    print('Who are you?')
    name = input()
    if name != 'Joe':
        continue
    print('Hello, Joe. What is the password? (It is a fish.)')
    password = input()
    if password == 'swordfish':
        break
print('Access granted.')

Who are you?
Who are you?
Hello, Joe. What is the password? (It is a fish.)
Who are you?
Hello, Joe. What is the password? (It is a fish.)
Access granted.

for <variable> in <sequence>:
    <statements>
else:
    <statements>

for i in range(3,11,2):
    print(i)

# 对列表循环
names = ['Michael', 'Bob', 'Tracy']
for name in names:
    print("Hello, %s"% name)

Hello, Michael
Hello, Bob
Hello, Tracy

# 对字符串循环
string = 'ABCDEFGHIJKLMNOPQRSTUVWXXYZ'
for letter in string:
    print(letter)
else:
    print("Finally finished!")

A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
X
Y
Z
Finally finished!

# 计算 1 + 2 + ... + 100
result = 0
for i in range(1,101):
    result = result + i
print(result)

print(sum(list(range(101))))

5050
5050

# 利用 for 循环生成列表
[1/i for i in range(1,10,3)]

[1.0, 0.25, 0.14285714285714285]

# 计算 1 - 2 + 3 -... -100
sum([row*(-1)**(row+1) for row in range(1,101)])

-50

# 找到 100 以内的质数（即不含除1和自身外为因数的数）
print([x for x in range(2,101) if True not in [x%y == 0 for y in range(2,x)]])

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

import module # 导入模块的所有部分
from module import name # 从模块中导入指定部分
from module import * # 导入模块的所有部分，且调用模块内的函数时不需要写模块名的前缀

import test
dir(test)

['__builtins__',
 '__cached__',
 '__doc__',
 '__file__',
 '__loader__',
 '__name__',
 '__package__',
 '__path__',
 '__spec__']

import random
for i in range(5):
    print(random.randint(1,10)) # 使用 random 模块的 randint 函数
    # 生成 1 ~ 10 之间的随机整数（包含 1 和 10）

2
1
8
10
4

import sys
while True:
    print('Type exit to exit.')
    response = input()
    if response == 'exit':
        sys.exit()
    print('You typed ' + response + '.')

Type exit to exit.
You typed .
Type exit to exit.
You typed a.
Type exit to exit.

An exception has occurred, use %tb to see the full traceback.

SystemExit

3. 控制流语句¶

3.1 if 语句¶

3.2 match 语句¶

3.3 while 循环语句¶

3.4 for 循环语句¶

3.5 补充：标准库¶

3.6 References¶