The second learning python and logic to determine if statements

Determination defined

If the conditions are met , in order to do something,
If the conditions are not met , it is another thing to do, or do nothing

Judge sentences also known as "branch statement," It is because of judgment, just let the program has a lot of branches

if the judge sentences the basic syntax

In Python the, IF statement is used for determination, the following format:

if 要判断的条件:
    条件成立时，要做的事情
    ……

Note: indent your code for a tab key, or 4 spaces - recommended space

In Python development, Tab and space do not mix!

2.2 Statement exercise judgment - judgment Age

demand

The definition of an integer variable age of record
To determine whether at least 18 years of age ( > = )
If the age of 18, allowed into the cafe Hi skin

# 1. 定义年龄变量
age = 18

# 2. 判断是否满 18 岁
# if 语句以及缩进部分的代码是一个完整的代码块
if age >= 18:
    print("可以进网吧嗨皮……")

# 3. 思考！- 无论条件是否满足都会执行
print("这句代码什么时候执行?")

Note :

if Statements, and the indented portion is a complete block of code

2.3 else case where the processing condition is not met

In use if when the judge can do to do things the conditions are met. If you need it , when the conditions are not satisfied , do certain things, how to do it?

answer

elseIn the following format:

if 要判断的条件:
    条件成立时，要做的事情
    ……
else:
    条件不成立时，要做的事情
    ……

Note :

if And else statements and respective indented portions together is a complete code block

2.4 Statement exercise judgment - judgment Age improvement

demand

Enter the user's age
To determine whether at least 18 years of age ( > = )
If the age of 18, allowed into the cafe Hi skin
If you are under 18 years of age, suggesting that home homework

# 1. 输入用户年龄
age = int(input("今年多大了？"))

# 2. 判断是否满 18 岁
# if 语句以及缩进部分的代码是一个完整的语法块
if age >= 18:
    print("可以进网吧嗨皮……")
else:
    print("你还没长大，应该回家写作业！")

# 3. 思考！- 无论条件是否满足都会执行
print("这句代码什么时候执行?")

logic operation

Program development, typically in the judgment conditions , a plurality of determination conditions will need to
Only a plurality of conditions are satisfied, it is possible to execute the subsequent code, the need to use the logical operators
Logical operators can put a plurality of conditions in accordance with the logic for the connection , it becomes more complex conditions
Python is logical operators include: and and / or or / Non not three kinds

1 `and`

条件1 and 条件2

And / and
Two conditions are met, return True
As long as there is not met, it returns False

Condition 1	Condition 2	result
Set up	Set up	Set up
Set up	Failure	Failure
Failure	Set up	Failure
Failure	Failure	Failure

2 `or`

条件1 or 条件2

Or / or
As long as there is a satisfying two conditions, return True
Two conditions are not satisfied, return False

Condition 1	Condition 2	result
Set up	Set up	Set up
Set up	Failure	Set up
Failure	Set up	Set up
Failure	Failure	Failure

3 `not`

not 条件

Non / not

condition	result
Set up	Failure
Failure	Set up

The if statement Advanced

1 `elif`

In the development, use if can be determined conditions
Use else can handle conditions are not met conditions
However, if you want to add a number of conditions , different conditions, different code needs to be executed when you can use elif
Syntax is as follows:

if 条件1:
    条件1满足执行的代码
    ……
elif 条件2:
    条件2满足时，执行的代码
    ……
elif 条件3:
    条件3满足时，执行的代码
    ……
else:
    以上条件都不满足时，执行的代码
    ……

Comparative logical operator code

if 条件1 and 条件2:
    条件1满足 并且 条件2满足 执行的代码
    ……

note

elif And else both must be if used in conjunction with, but not alone
It may be if, elif and else and each indent code, as a complete block of code

2 `if` Nested

elif scenario is: simultaneously determining a plurality of conditions , all the conditions are same level of

In the development, the use of if conditional judgment, if you want the conditions established in the implementation of the statement and then add conditions to judge , you can use nested if the
if nesting application scenario is: the premise condition is satisfied before, and then additional Analyzing
Nested if the syntax format, in addition to indent and before there is no difference
Syntax is as follows:

if 条件 1:
    条件 1 满足执行的代码
    ……
    
    if 条件 1 基础上的条件 2:
        条件 2 满足时，执行的代码
        ……    
        
    # 条件 2 不满足的处理
    else:
        条件 2 不满足时，执行的代码
        
# 条件 1 不满足的处理
else:
    条件1 不满足时，执行的代码
    ……

if nesting Walkthrough - Station security

The definition of a Boolean variable has_ticket indicating whether or not the ticket
Definition of an integer variable knife_length represented knife length, unit: cm
First, check for tickets, if any, are allowed to carry out security checks
When security is required to check the length of the knife, it is determined whether or not more than 20 cm
- If more than 20 cm, length of the blade tips are not allowed on the train
- If no more than 20 cm, by screening
If no ticket, do not allow the door

# 定义布尔型变量 has_ticket 表示是否有车票
has_ticket = True

# 定义整数型变量 knife_length 表示刀的长度，单位：厘米
knife_length = 20

# 首先检查是否有车票，如果有，才允许进行 安检
if has_ticket:
    print("有车票，可以开始安检...")

    # 安检时，需要检查刀的长度，判断是否超过 20 厘米
    # 如果超过 20 厘米，提示刀的长度，不允许上车
    if knife_length >= 20:
        print("不允许携带 %d 厘米长的刀上车" % knife_length)
    # 如果不超过 20 厘米，安检通过
    else:
        print("安检通过，祝您旅途愉快……")

# 如果没有车票，不允许进门
else:
    print("大哥，您要先买票啊")

Integrated application - rock-paper-scissors

Input from the console to the boxing - a stone (1) / scissors (2) / fabric (3)
Computer random punches - just a stone presuppose computer, complete the overall function of the code
Comparison of outcome

No.	rule
1	Rock wins scissors
2	Scissors wins cloth
3	Cloth win stone

1 Basic code implementation

First assume that the computer will only be a stone , to complete the overall function of the code

# 从控制台输入要出的拳 —— 石头（1）／剪刀（2）／布（3）
player = int(input("请出拳 石头（1）／剪刀（2）／布（3）："))

# 电脑 随机 出拳 - 假定电脑永远出石头
computer = 1

# 比较胜负
# 如果条件判断的内容太长，可以在最外侧的条件增加一对大括号
# 再在每一个条件之间，使用回车，PyCharm 可以自动增加 8 个空格
if ((player == 1 and computer == 2) or
        (player == 2 and computer == 3) or
        (player == 3 and computer == 1)):

    print("噢耶！！！电脑弱爆了！！！")
elif player == computer:
    print("心有灵犀，再来一盘！")
else:
    print("不行，我要和你决战到天亮！")

Processing the second random number

In Python , to use the random number, first you need to import a random number of modules - "toolkit"

import random

After import module, can be directly module name knocking behind a . press Tab button, will prompt all the functions included in the module
random.randint(a, b) Returns [a, b] an integer between, comprising a and b
E.g:

random.randint(12, 20)  # 生成的随机数n: 12 <= n <= 20   
random.randint(20, 20)  # 结果永远是 20   
random.randint(20, 10)  # 该语句是错误的，下限必须小于上限