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)