if语句的使用
在Python中，要构造分支结构可以使用if、elif和else关键字。所谓关键字就是有特殊含义的单词，像if和else就是专门用于构造分支结构的关键字，很显然你不能够使用它作为变量名（事实上，用作其他的标识符也是不可以）。
?for-in循环
sum = 0
for x in range(101):
??? sum += x
print(sum)
需要说明的是上面代码中的range类型，range可以用来产生一个不变的数值序列，而且这个序列通常都是用在循环中的，例如：
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range(101)可以产生一个0到100的整数序列。
-
range(1,100)可以产生一个1到99的整数序列。
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range(1,100,2)可以产生一个1到99的奇数序列，其中的2是步长，即数值序列的增量
while循环
如果要构造不知道具体循环次数的循环结构，我们推荐使用while循环。while循环通过一个能够产生或转换出bool值的表达式来控制循环，表达式的值为True循环继续，表达式的值为False循环结束。下面我们通过一个“猜数字”的小游戏（计算机出一个1~100之间的随机数，人输入自己猜的数字，计算机给出对应的提示信息，直到人猜出计算机出的数字）来看看如何使用while循环。
?
a,b,c=map(float,input(‘Enter a,c:‘).split(‘,‘))
sum = b**2 - 4*a*c
r1=(-b+sum**0.5)*0.5
r2=(-b-sum**0.5)*0.5
if sum > 0:
??? print("The roots are {0} and {1}".format(r1,r2))
elif sum < 0:
??? print("The root is {0}".format(-b * 0.5*a))
else:
??? print("The equation has no real roots")
?
?import random
answer1 = random.randint(1,100)
answer2 = random.randint(1,100)
number = float(input("输入整数的和：>>>>>"))
sum=answer1+answer2
if number == sum:
??? print("Ture")
else:
??? print("False")
city = [‘星期日‘,‘星期一‘,‘星期二‘,‘星期三‘,‘星期四‘,‘星期五‘,‘星期六‘]
Today = int(input(‘Today is :‘))
num_day = int(input(‘Number of days :‘))
day = num_day%7
if (Today+day)<7:
??? print(‘Future day is: %s‘%city[Today+day])
if (Today+day)==7:
??? print(‘Future day is: %s‘%city[0])
if Today+day>7:
??? print(‘Future day is: %s‘%city[Today+day-7])
num1,num2,num3 = eval(input("输入三个整数："))
if num1 > num2 > num3:
??? print(num1,num3)
if num1 > num3 > num2:
??? print(num1,num3,num2)
if num2 > num1 > num3:
??? print(num2,num1,num3)
if num2 > num3 > num1:
??? print(num2,num1)
if num3 > num2 > num1:
??? print(num3,num1)???
if num3 > num1 > num2:
??? print(num3,num2)
weight,packsge=eval(input("输入重量和价格："))
weight_1,packsge_1=eval(input("输入重量和价格："))
sum1 = packsge / weight
sum2 = packsge_1 / weight_1
if sum1 > sum2:
??? print("2")
else:
??? print("1")
mounthy,year=eval(input("输入月和年："))
if? year % 4 == 0 and year % 100 !=0? or year % 400 ==0:
??? if mounthy == 2:
??????? print("29")
??? elif mounthy == 4:
??????? print("30")
??? elif mounthy == 6:
??????? print("30")
??? elif mounthy == 9:
??????? print("30")
??? elif mounthy == 11:
??????? print("30")
??? else:
??????? print("31")
else:
??? if mounthy == 4:
??????? print("30")
??? elif mounthy == 6:
??????? print("30")
??? elif mounthy == 9:
??????? print("30")
??? elif mounthy == 11:
??????? print("30")
??? else:
??????? print("31")
import numpy as np
res = np.random.choice([‘正面‘,‘反面‘])
my = input("正面，反面：")
if my in ‘正面，反面‘:
???
??? if my == res:
??????? print("正确！")
??? else:
??????? print("错误！")
print(my)
print(res)
?
?import numpy as np
res = np.random.choice([‘0‘,‘1‘,‘2‘])
my = input("0，1，2：")
if my in ‘0，1，2‘:
??? if my == "0":
??????? if res == "0":
??????????? print("over")
??????? elif res == "1":
??????????? print("res win")
??????? elif res == "2":
???????????? print("my win")?
??? if? my == "1":
??????? if res == "0":
??????????? print("my win")
??????? elif res == "1":
??????????? print("over")
??????? elif res == "2":
???????????? print("res win")
??? if my =="2":
??????? if res == "0":
??????????? print("res win")
??????? elif res == "1":
??????????? print("my win")
??????? elif res == "2":
???????????? print("over")
print("电脑出：",res)
print("我出：",my)
?
?import math
year,m,q=map(int,input(‘请输入年月日【逗号隔开】‘).split(‘,‘))
j=math.floor(year/100)
k=year%100
h=(q+math.floor(26*(m+1)/10)+k+math.floor(k/4)+math.floor(j/4)+5*j)%7
week=[‘星期六‘,‘星期日‘,‘星期五‘]
print(‘Day of the week is %s‘%week[h])
import numpy as np
res = np.random.choice([‘A‘,‘2‘,‘3‘,‘4‘,‘5‘,‘6‘,‘7‘,‘8‘,‘9‘,‘10‘,‘j‘,‘q‘,‘k‘])
my = np.random.choice([‘梅花‘,‘红桃‘,‘方块‘,‘黑桃‘])
if my in ‘梅花，红桃，方块，黑桃‘:
??? if my == "梅花":
??????? print(my+res)
??? if my == "红桃":
??????? print(my+res)
??? if my == "方块":
??????? print(my+res)
??? if my == "黑桃":
??????? print(my+res)
?
number=float(input("一个三位数："))
ge = int(number %10)
shi = int(number /10%10)
bai = int(number /100)
if ge == bai:
??? print("{0}是回文数！".format(number))
else:
??? print("不是回文数！！！")
a,c=eval(input("三个数:"))
if a + b >c and b + c > a and a + c > b:
??? sum=a+b+c
??? print(sum)
else:
??? print("三边不合法")
?
?
今天学习分支结构和循环结构
