格式化输出的三种方式,运算符及流程控制之if判断

'''

格式化输出的三种方式,运算符及流程控制之if判断

'''

# 格式化输出的三种方式

# 一.占位符

程序中经常会有这样场景：要求用户输入信息，然后打印成固定的格式

比如要求用户输入用户名和年龄，然后打印如下格式：`My name is xxx，my age is xxx.`

很明显，用逗号进行字符串拼接，只能把用户输入的名字和年龄放到末尾，无法放到指定的xxx位置，而且数字也必须经过str(数字)的转换才能与字符串进行拼接，非常之麻烦，我们来试一试。

```
age = 19
print('My name is xxx，my age is '+str(age))
My name is xxx，my age is 19
age = 19
print('My name is xxx，my age is', age)
My name is xxx，my age is 19
name = 'nick'
age = 19
print('My name is '+name+' my age is '+str(age))
My name is nick my age is 19
```

上面使用的方法越看越别扭，越看越麻烦。这就需要用到占位符，如：%s（针对所有数据类型）、%d（仅仅针对数字类型）

```
name = 'nick'
age = 19
print('my name is %s my age is %s' % (name, age))
my name is nick my age is 19
age = 19
print('my age is %d' % age)
my age is 19
```

**二、format格式化**

```
name = 'nick'
age = 19
print("Hello, {}. You are {}.".format(name, age))
Hello, nick. You are 19.
name = 'nick'
age = 19
print("Hello, {1}. You are {0}-{0}.".format(age, name))
Hello, nick. You are 19-19.
name = 'nick'
age = 19
print("Hello, {name}. You are {age}-{age}.".format(age=age, name=name))
Hello, nick. You are 19-19.
```

**三、f-String格式化**

```
name = "nick"
age = 19
print(f"Hello, {name}. You are {age}.")
Hello, nick. You are 19.
```

大写的F也适用。

```
name = "nick"
age = 19
print(F"Hello, {name}. You are {age}.")
Hello, nick. You are 19.
age = 19
print(f'{age*2}')
38
```

**再给你秀个以后可能会用到的操作。**

```
salary = 6.6666
print(f'{salary:.2f}')
6.67
```

# 基本运算符

当我们眼前飘过一只生物后，我们会立即获得这个生物的信息，种类、性别、身高、三维，当我们获取这些信息的同时，我们还会马上对这些信息做一些逻辑处理，如这个生物种类是老虎的时候，我们会跑开；这个生物是人，性别为女，但是身高只有一米三时，我们可能会不自觉地靠近？

**一、算术运算符**

```
print(1+2)
3
x = 10
y = 20
res = x+y
print(res)
30
# /有零有整除，得到一个浮点型
print(10/3)
3.3333333333333335
# 地板除，只取整数部分
print(10//3)
print(10//4)
3
2
# %：取余
print(10 % 3)
1
# **，幂
print(10**3)
1000
```

[![029-基本运算符-算术运算符.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-%E7%AE%97%E6%9C%AF%E8%BF%90%E7%AE%97%E7%AC%A6.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-算术运算符.jpg?x-oss-process=style/watermark)

**二、比较运算符**

[![029-基本运算符-比较运算符.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-%E6%AF%94%E8%BE%83%E8%BF%90%E7%AE%97%E7%AC%A6.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-比较运算符.jpg?x-oss-process=style/watermark)

```
pwd = '123'
print(pwd != '123')
print(pwd == '123')
False
True
l1 = [1, 'a', 3]
l2 = [3]
print(l1 < l2)  # False
True
try:
    l3 = [1, 3]
    print(l1 < l3)  # 报错，列表比较大小仅限于同一位置的对应的值是相同的类型
except Exception as e:
    print(e)
name 'l1' is not defined
```

**三、赋值运算符**

[![029-基本运算符-赋值运算符.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-%E8%B5%8B%E5%80%BC%E8%BF%90%E7%AE%97%E7%AC%A6.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-赋值运算符.jpg?x-oss-process=style/watermark)

```
age = 19
age = age + 1
print(age)
20
age = 19
age += 1
print(age)
20
age = 19
age *= 10
print(age)
190

```

**四、逻辑运算符**

[![029-基本运算符-逻辑运算符.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-%E9%80%BB%E8%BE%91%E8%BF%90%E7%AE%97%E7%AC%A6.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-逻辑运算符.jpg?x-oss-process=style/watermark)

```
# 从左到右的方式找到逻辑运算符，找到逻辑运算符的左边，左边成立，再去找到逻辑运算符的右边
print(3 > 3 and 1 > 2 or 2 > 1)  # False
True

```

**五、身份运算符**

[![029-基本运算符-身份运算符.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-%E8%BA%AB%E4%BB%BD%E8%BF%90%E7%AE%97%E7%AC%A6.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-身份运算符.jpg?x-oss-process=style/watermark)

is和==的区别：is用于判断两个变量引用对象是否为同一个(是否在同一块内存空间中)， ==用于判断引用变量的值是否相等。

```
x = 257
y = x
z = 257

print(f'x is y:{x is y}')
print(f'x == y:{x == y}')

print(f'x is z:{x is z}')
print(f'x == z:{x == z}')
x is y:True
x == y:True
x is z:False
x == z:True

```

**六、Python运算符优先级**

```
# Python中True为1，False为0
print(True > 0)  # True
print(True > 2)  # Flase

```

[![029-基本运算符-python运算符优先级.jpg?x-oss-process=style/watermark](http://www.chenyoude.com/Python%E4%BB%8E%E5%85%A5%E9%97%A8%E5%88%B0%E6%94%BE%E5%BC%83/029-%E5%9F%BA%E6%9C%AC%E8%BF%90%E7%AE%97%E7%AC%A6-python%E8%BF%90%E7%AE%97%E7%AC%A6%E4%BC%98%E5%85%88%E7%BA%A7.jpg?x-oss-process=style/watermark)](http://www.chenyoude.com/Python从入门到放弃/029-基本运算符-python运算符优先级.jpg?x-oss-process=style/watermark)

# 流程控制之if判断

## 一.语法

if判断是干什么的呢？if判断其实是在模拟人做判断。就是说如果这样干什么，如果那样干什么。对于ATM系统而言，则需要判断你的账号密码的正确性。

**1.1 if**

```
if 条件:
    代码1
    代码2
    代码3
    ...
# 代码块(同一缩进级别的代码，例如代码1、代码2和代码3是相同缩进的代码，这三个代码组合在一起就是一个代码块，相同缩进的代码会自上而下的运行)
cls = 'human'
gender = 'female'
age = 18

if cls == 'human' and gender == 'female' and age > 16 and age < 22:
    print('开始表白')

print('end...')
开始表白
end...

```

**1.2 if...else**

if...else表示if成立代码成立会干什么，else不成立会干什么。

```
cls = 'human'
gender = 'female'
age = 38

if cls == 'human' and gender == 'female' and age > 16 and age < 22:
    print('开始表白')
else:
    print('阿姨好')
阿姨好

```

**1.3 if...elif...else**

if...elif...else表示if条件1成立干什么，elif条件2成立干什么，elif条件3成立干什么，elif...否则干什么。

```
cls = 'human'
gender = 'female'
age = 28

if cls == 'human' and gender == 'female' and age > 16 and age < 22:
    print('开始表白')
elif cls == 'human' and gender == 'female' and age > 22 and age < 30:
    print('考虑下')
else:
    print('阿姨好')
考虑下

```

**二、if的嵌套**

```
# if的嵌套
cls = 'human'
gender = 'female'
age = 18
is_success = False

if cls == 'human' and gender == 'female' and age > 16 and age < 22:
    print('开始表白')
    if is_success:
        print('那我们一起走吧...')
    else:
        print('我逗你玩呢')
else:
    print('阿姨好')
开始表白
我逗你玩呢

```

**三、练习**

```
# 成绩评判
score = input("your score: ")
score = int(score)

if score >= 90:
    print('优秀')
# elif score >= 80 and score < 90:
elif score >= 80:
    print('良好')
# elif score >= 70 and score < 80:
elif score >= 70:
    print('普通')
else:
    print('差')
your score: 80
良好

```

**3.2 练习2：模拟登录注册**

```
username: nick
password: 123
username or password error

```