变量与数据类型
# 动态类型，不需要声明
name = "Alice"
age = 25
height = 1.68
is_student = True
# 类型检查
print(type(name)) # <class 'str'>
print(isinstance(age, int)) # True
# 基本类型
int_val = 42
float_val = 3.14
str_val = "hello"
bool_val = False
none_val = None # 空值
# 多变量赋值
a, b = 1, 2
x = y = z = 0 # 三个都是 0
# f-string（Python 3.6+）
print(f"{name} is {age} years old")
容器类型
# 列表 list — 可变有序
fruits = ["apple", "banana", "cherry"]
fruits.append("orange")
fruits.insert(1, "grape")
fruits.remove("banana")
print(fruits[0]) # apple
print(fruits[-1]) # 最后一个
print(fruits[1:3]) # 切片 [1, 3)
# 列表推导式
squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]
# 元组 tuple — 不可变
point = (3, 4)
x, y = point # 解包
single = (1,) # 单元素元组，逗号不能丢
# 字典 dict — 键值对
user = {"name": "Bob", "age": 30}
user["email"] = "bob@example.com"
print(user.get("phone", "N/A")) # 安全取值
# 字典推导式
squares_map = {x: x**2 for x in range(5)}
# 集合 set — 不重复无序
tags = {"python", "coding", "python"} # {"python", "coding"}
tags.add("tutorial")
print("python" in tags) # True
控制流
# if-elif-else
score = 85
if score >= 90:
grade = "A"
elif score >= 80:
grade = "B"
else:
grade = "C"
# for 循环
for i in range(5): # 0..4
print(i)
for fruit in fruits: # 遍历可迭代对象
print(fruit)
for i, fruit in enumerate(fruits): # 带索引
print(f"{i}: {fruit}")
for k, v in user.items(): # 字典遍历
print(f"{k} = {v}")
# while
count = 0
while count < 5:
print(count)
count += 1
# break / continue
for x in range(10):
if x == 3:
continue # 跳过 3
if x == 7:
break # 到 7 停止
print(x) # 输出 0 1 2 4 5 6
函数
def greet(name, greeting="Hello"):
"""返回问候语""" # docstring
return f"{greeting}, {name}!"
print(greet("Alice")) # Hello, Alice!
print(greet("Bob", "Hi")) # Hi, Bob!
# 可变参数
def sum_all(*args):
return sum(args)
print(sum_all(1, 2, 3, 4)) # 10
# 关键字参数
def create_user(**kwargs):
for k, v in kwargs.items():
print(f"{k}: {v}")
create_user(name="Alice", age=25)
# Lambda
square = lambda x: x ** 2
sorted(fruits, key=lambda f: len(f)) # 按长度排序
类
class Animal:
species = "Unknown" # 类变量
def __init__(self, name): # 构造方法
self.name = name # 实例变量
def speak(self):
return f"{self.name} makes a sound"
class Dog(Animal):
species = "Canine" # 覆盖类变量
def __init__(self, name, breed):
super().__init__(name) # 调用父类构造
self.breed = breed
def speak(self):
return f"{self.name} barks!"
dog = Dog("Rex", "Labrador")
print(dog.speak()) # Rex barks!
print(isinstance(dog, Animal)) # True
模块与导入
# 导入
import math
from datetime import datetime, timedelta
from pathlib import Path
import numpy as np # 别名
print(math.sqrt(16)) # 4.0
# 文件操作
with open("file.txt", "r") as f:
content = f.read()
with open("output.txt", "w") as f:
f.write("Hello")
# Pathlib（推荐替代 os.path）
path = Path("data/config.json")
print(path.suffix) # .json
print(path.parent) # data
text = path.read_text()