Python的基本语法2

一.运算符

# 算术运算符, +,  -,  *,  /,  //,  %,  **,  注意//为整除
# 赋值运算符, =, +=, -=, *=, /=, //= ,%=, **=
# 比较运算符, ==, !=, <>, >, >=, <, <=
# 逻辑运算符, and, or, not
# 成员运算符, in, not in
# 身份运算符, is, not is
# 位运算符,   &, |, >>, <<, ^, ~

# 优先级  算术>比较>逻辑>赋值

a = 3
b = 5
print(b // a)  # 1
a *= 3  # 9
print(a > b)  # True,9>5
print(3>4 and 4>2)  # False

二.判断语句

(1)if单分支

if 条件表达式:

  command1

  ...

执行顺序:如果条件表达式为真,就进行command1...

# 单分支
if 3 > 5:
    print("oh,my gold,it's impossible.")

(2)if双分支

if 条件表达式1:

  command1

  ...

else:

  command2

  ...

执行顺序:如果条件表达式1为真,就执行command1...;条件表达式1为假,就执行command2...

# 双分支
if 3 > 5:
    print("hehe~")
else:
    print("3<5 is true")

(3)多分支

if 条件表达式1:

  command1

  ...

elif 条件表达式2:

  command2

  ...

else:

  command n

  ...

执行顺序:条件表达式1为真,则执行command1,否则判断条件表达式2,条件表达式2为真,则执行command2...;如果都为假,则执行else下的command n

# 多分支及嵌套
age = input("pls type your age:")
sex = input("pls type your sex:")
if int(age) < 0:
    print("you type wrong age.pls input again.")
elif int(age) < 18:
    print("it's a boy.")
else:
    if sex == "man" or sex == "male":    # or为或者的意思
        print("you are %s years old, is a %s" % (age, sex))
    elif sex == "woman" or sex == "female":
        print("you are {} years old ,is a {}".format(age, sex))
    else:
        print("you type wrong sex,pls input again")

三.while循环

while 条件表达式:

  command1

  ...

 

执行顺序:

条件表达式为真,就执行循环体中的命令,一轮循环结束后,再次判断条件表达式,如果为真,就再次进入循环,直到条件表达式为假,就退出循环

循环控制语句

continue 结束本次循环,开始下一轮循环

break 跳出循环(如果有循环嵌套,要注意break的位置,是跳出内循环还是外循环)

exit() 退出python程序,可以指定返回值

 示例:

# 猜数字小游戏
import random
number = random.randint(1, 100)  # 获取1~100的随机数,包括1和100

while True:
    guess_num = int(input("pls type a number(1-100):"))
    if guess_num > number:
        print("you guess big.pls guesss again.")
        continue
    elif guess_num < number:
        print("you guess small.pls guess again")
        continue
    else:
        print("success,it's {}.".format(guess_num), "you will get a prize")
        flag = input("do you want play again?(y/n):")
        if flag == "y":
            number = random.randint(1, 100)
            continue
        else:
            break
# while practice

# 打印100以内的偶数之和

# 方法一
i = 0
sum = 0
while i <= 100:
    sum += i
    i += 2
print("sum = %d" % sum)

# 方法二
i = 0
sum = 0
while i <= 100:
    if i%2 == 0:
        sum += i
    i += 1
print("sum = %d" % sum)

# 方法三
i = 0
sum = 0
while i <= 100:
    if i%2 == 1:
        i += 1
    else:
        sum += i
        i += 1
print("sum = %d" % sum)
posted @ 2019-04-24 21:04  sxlong_work  阅读(238)  评论(0编辑  收藏  举报