📚 Python语言的特点

1. ✅ 简单易学
2. ✅ 免费开源
3. ✅ 面向对象
4. ✅ 可移植性
5. ✅ 可扩展性
6. ✅ 丰富的库
7. ✅ 规范的代码
8. ✅ 动态语言特点

🏷️ 变量命名

命名惯例

命名规则

• ❌ 变量名不能以数字开头
• ⚠️ 变量名区分大小写 (total ≠ Total)
• 🔒 双下划线开头的变量为私有变量

2cats = 10  # 错误
_cats = 10  # 可以
hey@hey = 10  # 不推荐

cats != CATS  # 大小写不同

📦 数据类型

# 布尔值
x = True 

# 整数
y = 1 

# 字符串
z = "Hello World"

# 列表
numbers = [1, 2, 3, 'four'] 

# 元组
letters = ('a', 'b', 'c', 'd') 

🔤 字符串详解

字符串定义

str1 = 'Hello, world!'
str2 = "Hello, world!"
str3 = '''Hello, 
            world!'''
str4 = """Hello, 
            world!"""

字符串格式化

miles = "10"

print('%s %s' % ('Hello', 'world'))
print('只有一个{}*'.format(1,2))  # 默认占位
print('{0}*{0}+{1}'.format(1,2))  # 数字占位
print('{a1}*{a1}+{a2}'.format(a1=2,a2=3))  # 参数占位
print("Today you ran {0} miles. Good Job".format(miles))
print(f"Today you ran {miles} miles. Good Job")  # f-string格式化

原始字符串和字节串

# 原始字符串 (r前缀)
my_string_r = r'\nTest\n'  # 转义字符不生效

# 字节串 (b前缀)
my_string_b = b'hello'  # 字节序列

编码转换

# 字符转Unicode编码
hex(ord('中'))  # '0x4e2d'

# 字符转UTF-8编码
'中'.encode('utf-8')  # b'\xe4\xb8\xad'

# Unicode编码还原成字符
chr(0x4e2d)  # '中'

# UTF-8编码还原成字符
b'\xe4\xb8\xad'.decode('utf-8')  # '中'

🔍 正则表达式

常用元字符

常用匹配模式

import re

# 匹配邮政编码
postcode = '100101'
pattern = r'\d{6}'
result = re.match(pattern, postcode)

# 匹配身份证号码
idcard = '110101199001011234'
pattern = r'\d{17}[\dXx]'
result = re.search(pattern, idcard)

# 匹配手机号码
phone = '13912345678'
pattern = r'1\d{10}'
result = re.search(pattern, phone)

# 匹配邮箱地址
email = 'abc@xyz.com, def@xyz.com'
pattern = r'\w+@\w+\.[a-z]{2,3}'
result = re.findall(pattern, email)

# 替换字符串
text = 'Hello, world!'
pattern = r'world'
result = re.sub(pattern, 'Python', text)

➕ 运算符

算术运算符

print(10*2)    # 乘法
print(10**2)   # 平方
print(10/2)    # 除法（返回浮点数）
print(10//2)   # 整除
print(10%2)    # 取模

比较运算符

print(10>2)    # 大于
print(10<2)    # 小于
print(10>=2)   # 大于等于
print(10<=2)   # 小于等于
print(10==2)   # 等于
print(10!=2)   # 不等于

逻辑运算符

a = 0
if a and a == 2 and a > 10:
    print("条件都为True")
    
if a or b:
    print("至少一个为True")
    
if not(a and b):
    print("取反")

成员运算符

a = 10
list = [1, 2, 3, 4, 5]

if a in list:
    print("a在列表中")
    
if a not in list:
    print("a不在列表中")

身份运算符

a = [1,2,3]
b = [1,2,3]

print(a == b)  # True - 值相等
print(a is b)  # False - 不是同一对象

🔀 条件语句

from random import *
x = randint(1,20)

if x < 18:
    print('Sorry You are too young')
elif x >= 18 and x <= 21:
    print('You are allowed to go')
else:
    print('You are old enough for this')

🔄 循环语句

while循环

import random

min = 1
max = 6
roll_again = "yes"

while roll_again in ("yes", "y"):
    print("Rolling the dices...")
    print(random.randint(min, max))
    roll_again = input("Roll again?").strip().lower()

for循环

for x in range(1,10):
    if x == 9:
        break
    elif x == 5:
        continue
    else:
        print(x)

📋 列表操作

shopping_list = []
shopping_list.append("item")
shopping_list.extend([5,6,7,8])
shopping_list.insert(1, 'hi')
shopping_list.pop()
shopping_list.remove(1)
shopping_list.reverse()
shopping_list.sort()

# 切片
x = [1,2,3,4,5,6]
print(x[0:2])      # [1,2]
print(x[0:7:2])    # [1,3,5]

# 列表推导式
y = [x*x for x in range(10) if x%2==0]

📦 元组操作

x = (1,2,3,4,5)
x.count(1)   # 统计出现次数
x.index(1)   # 查找索引

📖 字典操作

info = {
    'name': 'John',
    'city': 'New York',
    'own_a_car': True,
}

print(info.get('name'))
print(info['name'])

for key, value in info.items():
    print(key, value)
    
# 字典推导式
a = dict(a=1,b=2,c=3)
b = {key: value**2 for key, value in a.items()}

🎯 集合操作

my_set = {1, 'apple', 10.5}
my_set.add('banana')
my_set.remove('apple')
my_set.discard('apple')  # 不存在不报错

a = {1,2,3,4}
b = {2,3,5}
print(a | b)  # 并集
print(a & b)  # 交集

# 不可变集合
my_frozen_set = frozenset(my_set)

🛠️ 函数定义

基本函数

def elo(player_rating, opponent_rating, won, k=32):
    q1 = 10**(player_rating / 400)
    q2 = 10**(opponent_rating / 400)
    expected_score = q1 / (q1 + q2)
    true_score = int(won)
    final_score = player_rating + k * (true_score - expected_score)
    return int(final_score)

位置参数和关键字参数

def example_function(arg1, arg2, kwarg=None):
    print(f"arg1: {arg1}")
    print(f"arg2: {arg2}")
    if kwarg:
        print(f"kwarg: {kwarg}")

example_function("a", "b")
example_function("a", "b", kwarg="c")
example_function(arg2="b", arg1="a", kwarg="c")

可变参数

def example_function(*args):
    for arg in args:
        print(arg)

example_function(1, 2, 3)

def example_function(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

example_function(name="Alice", age=30)

参数顺序

# 参数顺序: 位置参数 -> *args -> 默认参数 -> **kwargs
def odering(a, b, *args, name='john', **kwargs):
    return [a, b, args, name, kwargs]

🔄 迭代器

from collections.abc import Iterable, Iterator

# 判断是否可迭代
isinstance([], Iterable)      # True
isinstance({}, Iterable)      # True
isinstance('abc', Iterable)   # True

# 判断是否是迭代器
isinstance([], Iterator)      # False
isinstance(iter([]), Iterator)  # True

⚠️ 异常处理

try:
    x = int(input("Enter a number"))
except ValueError:
    print("Enter a valid Number")
except:
    print("Unknown error")
else:
    print("Thanks for a valid number")
finally:
    print("I will run no matter what")

🐛 PDB调试

常用PDB命令：

• l - 列表
• n - 下一行
• p - 打印
• c - 继续