python基础#

注释#

#/三引号"""……""" 多行注释

字符串与字符串连接#

字符串连接 +
```
1
print("Hello"+"World"+"!")
```

双单引号转义

1
 print('He said "good!"') # 单引号包裹 He said "good"
2
 print("He said 'good!'") # 双引号包裹 He said 'good'
3
 print("He said \"Let's go!\"") # 转义符 He said "Let's go!"

三引号跨行字符串自换行
```
1
print("""Hello
2
World""")
```

常用方法

1
 s = "hello"
2
 s.upper()    # 转大写 HELLO
3
 s.lower()    # 转小写
4
 s.strip()    # 去掉首尾空格
5
 s.replace("h", "H")  # 替换
6
 s.split(",") # 按符号分割成列表

格式化字符串#

format()

1
print("My name is {0},I'm {1} years old".format("Liz", 19))
2
 print("My name is {name},I'm {age} years old".format(name="Liz", age=19))
3
 name = "Yuzy"
4
 age = 20
5
 print(f"My name is {name},I'm {age} years old")

f-字符串

数据类型#

字符串 str

1
len("Hello") # 5
2
len("哟! ") # 2
3
len("\n") # 1

整型 int、浮点数 float

1
grade =93.546
2
 print("Your grade is: " + f"{grade:.2f}") # Your grade is: 93.55

布尔类型
type 输出数据类型

输入 input#

1
user_name = str(input("请输入用户名："))

条件判断语句#

1
grade = int(input("please input your grade: "))
2
if grade >= 90:
3
    print("A")
4
elif grade >= 80:
5
    print("B")
6
elif grade >= 65:
7
    print("C")
8
else:
9
    print("D")

循环语句#

1
constants = ("Alice", "Bob", "Charlie", "David", "Eve")
2
for contant in constants:
3
    print(contant)
4

5
for i in range(5,10):  # [5,10)
6
    print(i)
7
for i in range(5,10,2):  # 5 7 9 步长为2
8
    print(i)
9

10
i = 0
11
while i <len(constants):
12
    print(constants[i])
13
    i += 1

逻辑运算#

1
x = int(input("Enter a number: "))
2
print(not(x>5 and x<10)) # 6 -False;2 - True

列表 List#

有序、可重复、可扩展

1
shopping_list = ["milk", "eggs", "bread"]
2
shopping_list.append("bread") # ['milk', 'eggs', 'bread', 'bread']
3
shopping_list.remove("eggs") # ['milk', 'bread', 'bread']
4
len(shopping_list) # 3
5
print(shopping_list[1]) # eggs
6
print(shopping_list[0:2]) # ['milk', 'eggs']
7
print(shopping_list[0:2]) # ['milk', 'eggs']
8
shopping_list.insert(1, 15)  # 指定位置插入
9
shopping_list.pop()          # 删除最后一个
10
shopping_list.pop(0)         # 删除指定索引
11
shopping_list.clear()        # 清空
12
shopping_list.sort()         # 对于int排序
13
shopping_list.reverse()      # 反转
14
print(shopping_list)         # []

元组 Tuple#

有序、可重复、不可扩展，当作键使用

1
example_tuple = ("keyboard", "mouse", "monitor")
2
example_tuple.append("printer")  # ❌
3
example_tuple.remove("mouse")  # ❌
4
# 作为键
5
contacts = {
6
    ("Lily",19):"421880110",
7
    ("Bob",25):"421880111",
8
    ("Tom",30):"421880112"
9
}
10
print(contacts[("Lily",19)])  # 输出：421880110

集合 Set#

无序、不可重复、可扩展

1
names = {"Lily","Rose","Daisy","Iris"}
2
print("Lily" in names) # True
3
print(type(names)) # <class 'set'>

字典 {}#

键 : 值

1
contacts ={
2
    "Alice": "152-555-1234",
3
    "Bob": "152-555-5678",
4
}
5
print(contacts.get("Alice")) # 152-555-1234
6
print(contacts.get("Charlie")) # None
7
print(contacts["Alice"]) # Output: 152-555-1234
8
print("Bob" in contacts) # Output: True
9
# 删除键值对 del 字典名[键]
10
del contacts["Alice"]
11
print(len(contacts)) # Output: 1
12
# 遍历字典
13
for name in contacts:
14
    print(name, contacts[name])
15
# 所有键
16
print(contacts.keys()) # Output: dict_keys(['Bob'])
17
# 所有值
18
print(contacts.values()) # Output: dict_values(['152-555-5678'])
19
# 所有键值对
20
print(contacts.items()) # Output: dict_items([('Bob', '152-555-5678')])

模块#

继承很多功能的函数集合称作模块

1
# 自定义模块，导入module.py中的函数
2
import math
3
print(math.sqrt(16))
4
# 直接调用，不加模块名
5
from math import *
6
print(sqrt(16))
7
print(math.sqrt(16)) # math 本身没有被导入！NameError: name 'math' is not defined
8

9
# 导入内置模块
10
import random
11
num = random.randint(1, 100)
12
print(num)
13
random_list = [11,22,33,44]
14
data = random.choice(random_list)
15
print(data)
16

17
# from 模块名 import sqrt
18
from math import sqrt
19
print(sqrt(16))
20

21
# import 模块名 as 别名
22
import math as m
23
print(m.sqrt(16))

类 & 方法#

基本语法

1
class Dog:
2
 pass
3

4
 my_dog = Dog()          # 创建实例（对象）
5
 print(type(my_dog))     # <class '__main__.Dog'>

初始化方法__init__和实例属性
双下划线：私有属性

1
class Dog:
2
    def __init__(self, name, age):
3
        self.name = name   # 实例属性
4
        self.age = age
5

6
my_dog = Dog("旺财", 3)

魔术方法

1
class Cat:
2
    def __init__(self, name):
3
        self.name = name
4

5
    # 魔术方法：控制对象打印结果
6
    def __str__(self):
7
        return f"猫咪：{self.name}"
8

9
tom = Cat("汤姆")
10
print(tom)  # 自动执行 __str__，输出：猫咪：汤姆
11

12
class Book:
13
    def __len__(self):
14
        return 200  # 自定义页数
15

16
b = Book()
17
print(len(b))  # 自动调用 __len__，输出 200

实例方法

1
 class Dog:
2
     def __init__(self, name, age):
3
         self.name = name
4
         self.age = age
5

6
     def get_human_age(self):
7
         return self.age * 7
8

9
 my_dog = Dog("旺财", 3)
10
 human_age = my_dog.get_human_age()  # 21

类属性 vs 实例属性

1
class Dog:
2
    species = "Canis familiaris"   # 类属性
3

4
    def __init__(self, name):
5
        self.name = name            # 实例属性
6

7
dog1 = Dog("旺财")
8
dog2 = Dog("来福")
9
print(dog1.species)  # Canis familiaris
10
print(dog2.species)  # Canis familiaris
11
print(Dog.species)  # 直接通过类名查询：Canis familiaris
12
Dog.species = "狗"    # 修改类属性会影响所有实例
13
print(dog1.species)  # 狗

类方法
第一个参数是cls（类本身）

1
class Dog:
2
    total_dogs = 0
3

4
    def __init__(self, name):
5
        self.name = name
6
        Dog.total_dogs += 1
7

8
    @classmethod
9
    def get_total(cls):
10
        return cls.total_dogs
11

12
print(Dog.get_total())  # 0
13
d1 = Dog("旺财")
14
d2 = Dog("来福")
15
print(Dog.get_total())  # 2

静态方法和普通函数的区别是：不能访问实例属性或类属性

1
class MathUtils:
2
    @staticmethod
3
    def add(x, y):
4
        return x + y
5

6
print(MathUtils.add(3, 5))  # 8

继承#

基础格式

1
class Animal:
2
    ……
3
class Dog(Animal):
4
    ……

super()调用父类方法

1
class Cat(Animal):
2
 def speak(self):
3
     super().speak()      # 先调用父类方法
4
     print("喵喵喵")      # 再添加子类行为

属性封装&property#

Python 没有严格的私有属性，但约定以 _ 开头的属性为“保护”的，不应当直接访问。可以使用@property提供 getter/setter。

1
class Person:
2
    def __init__(self, name):
3
        # 私有属性，外部不直接访问
4
        self._name = name
5

6
    # 取值方法：对象.name 自动调用
7
    @property
8
    def name(self):
9
        return self._name
10

11
    # 赋值方法：对象.name = 值 自动调用
12
    @name.setter
13
    def name(self, val):
14
        # 简单校验
15
        if len(val) < 2:
16
            raise ValueError("名字太短")
17
        self._name = val
18

19
# 使用
20
p = Person("小明")
21
print(p.name)     # 调用@property，取值
22

23
p.name = "小红"    # 调用setter，赋值
24
print(p.name)