Python 学习2

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Python-if，while, for循环

key points

if语句，及if语句套用

  1. if…else
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name=input()  #显示输入框，name=输入内容 show the inputbox，name=input #input 函数
if name == 'Mary':               #if 语句
    print('Hello Mary')
    password=input()
    if password == 'swordfish':
        print('Access granted.')
    else:                        #if...else语句           
        print('Wrong password.')

该代码可判断用户名及密码是否与设定值相符

check the user‘s name and password

  1. if…elif
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name=input()
if name == 'Alice':
    print('Hi,Alice.')  
else:
    print('What is your age?')
    age=input()
    if age < '12':
        print('You are not Alice, kiddo.')
    elif age > '100':
        print('You are not Alice,grannie.')
    elif age > '2000':
        print('Unlike you, Alice is not an undead, immortal vampire.')

该代码通过判断年龄确定身份

check the user through age

while语句

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spam = 0
while spam < 5:
    print('Hello world!')
    spam = spam+1

output：

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Hello world!
Hello world!
Hello world!
Hello world!
Hello world!

‘break’ and ‘continue’

break:

When the break is executed, the loop ends.

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spam=0
while True:
    print('Hello world')
    if spam==3:
        break
    spam=spam+1
print(spam)

#out:
#Hello world
#Hello world
#Hello world
#Hello world
#3

continue:

When continue is executed, the loop starts again.

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spam=1
while spam<4:
    print('Hello!')
    spam=spam+1
    if spam==3:
        continue
    print('Hello world')
    print(' ')
print(spam)

#out:
#Hello!
#Hello world
#
#Hello!  during this time, spam=3, so it didn't print 'Hello world'.
#Hello!
#Hello world
#4

while+if

输入密码 input the password

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key=input() 
spam=0 #record the times tried, make sure no more than 3 times 不超过三次
if int(key)==12345:
        print('Pass')
while spam < 2 and int(key)!=12345:
            print('Try again')
            key=input()
            spam=spam+1  #计次 record thetimes
if int(key)==12345 and spam!=0:
        print('Pass')

e.g.

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>1
Try again
>12
Try again
>12345
Pass

another way：

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key=input()
if key=='12345':
    print('pass')
else:
    print('try again')
    key=input()
    if key=='12345':
        print('pass')
    else:
        print('try again')
        key=input()
        if key=='12345':
            print('pass')

for循环

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for i in range(12,16):
    print(i)

12到16的所有整数

print all integers in 12 to 16

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for i in range(0,10,2): #the 2 here means the step is 2
    print(i)
#out：0 2 4 6 8
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for i in range(5,-1,-1): 
    print(i)
#output：5 4 3 2 1 0

example

a tricky game：

You must input ‘your name’ instead of the real name:

你要输入 ”your name” 而不是真的名字

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print('Please type your name.')
yourname=input()
while  yourname!='your name':
    print('Please type your name.')
    yourname=input()
if yourname=='your name':
    print('Thank you!')

e.g.

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Please type your name.
Alice
Please type your name.
Emma
Please type your name.
your name
Thank you!

another way:

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while True:
    print('Please type your name.')
    name=input()
    if name == 'your name':
        break
print('Thank you!')

make patterns!

1

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a=6
while True:
    print('*'*a) #'*'is the string while * is 'x', multiply
    a=a-1 #the number of a is decreasing
    if a==0:
        break  #if there is no more '*', it ends

e.g.

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******
*****
****
***
**
*

2

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a=1
while True:
    print('*'*a) 
    a=a+1
    if a==6:
        break
while True:
    print('*'*a)
    a=a-1
    if a==0:
        break
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*
**
***
****
*****
******
*****
****
***
**
*

another way

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for a in range(1,7):
    print('*'*a)
for a in range(5,0,-1):
    print('*'*a)

calculation of factorial

阶乘计算

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result=1
a=int(input())
for i in range(1,a+1):
    result=result*i
print(result)

e.g.

input=9

output=362880