变量与数据类型
# 变量赋值
name = "Python"
version = 3.11
is_awesome = True
nothing = None
# 多重赋值
x, y, z = 1, 2, 3
# 类型检查
print(type(name)) # <class 'str'>
print(type(version)) # <class 'float'>字符串操作
# 字符串格式化
name = "World"
print(f"Hello, {name}!") # f-string (推荐)
print("Hello, {}!".format(name)) # format 方法
# 常用方法
text = " Hello, Python! "
print(text.strip()) # "Hello, Python!"
print(text.lower()) # " hello, python! "
print(text.upper()) # " HELLO, PYTHON! "
print(text.replace("Python", "World")) # " Hello, World! "
print(text.split(",")) # [' Hello', ' Python! ']列表推导式
# 基础列表推导式
squares = [x**2 for x in range(10)]
print(squares) # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
# 带条件的列表推导式
even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares) # [0, 4, 16, 36, 64]
# 嵌套列表推导式
matrix = [[i*j for j in range(1, 4)] for i in range(1, 4)]
print(matrix) # [[1, 2, 3], [2, 4, 6], [3, 6, 9]]
# 字典推导式
word = "hello"
char_count = {c: word.count(c) for c in set(word)}
print(char_count) # {'h': 1, 'e': 1, 'l': 2, 'o': 1}
# 集合推导式
unique_lengths = {len(word) for word in ["hello", "world", "python"]}
print(unique_lengths) # {5, 6}字典操作
# 创建字典
person = {
"name": "张三",
"age": 25,
"city": "北京"
}
# 获取值
print(person.get("name")) # "张三"
print(person.get("phone", "N/A")) # "N/A" (默认值)
# 遍历字典
for key, value in person.items():
print(f"{key}: {value}")
# 字典推导式
squares_dict = {x: x**2 for x in range(5)}
print(squares_dict) # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}函数
# 基础函数
def greet(name, greeting="Hello"):
return f"{greeting}, {name}!"
print(greet("World")) # "Hello, World!"
print(greet("World", "Hi")) # "Hi, World!"
# *args 和 **kwargs
def flexible(*args, **kwargs):
print(f"位置参数: {args}")
print(f"关键字参数: {kwargs}")
flexible(1, 2, 3, name="Python", version=3.11)
# 位置参数: (1, 2, 3)
# 关键字参数: {'name': 'Python', 'version': 3.11}
# Lambda 函数
add = lambda x, y: x + y
print(add(3, 5)) # 8
# 高阶函数
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))
print(squared) # [1, 4, 9, 16, 25]
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens) # [2, 4]装饰器
# 基础装饰器
def timer(func):
import time
def wrapper(*args, **kwargs):
start = time.time()
result = func(*args, **kwargs)
end = time.time()
print(f"{func.__name__} 执行时间: {end - start:.4f} 秒")
return result
return wrapper
@timer
def slow_function():
import time
time.sleep(1)
return "完成"
slow_function()
# 带参数的装饰器
def repeat(times):
def decorator(func):
def wrapper(*args, **kwargs):
for _ in range(times):
result = func(*args, **kwargs)
return result
return wrapper
return decorator
@repeat(times=3)
def say_hello():
print("Hello!")
say_hello() # 会打印 3 次 "Hello!"生成器
# 生成器函数
def fibonacci(limit):
a, b = 0, 1
while a < limit:
yield a
a, b = b, a + b
# 使用生成器
for num in fibonacci(100):
print(num, end=" ")
# 输出: 0 1 1 2 3 5 8 13 21 34 55 89
# 生成器表达式
squares_gen = (x**2 for x in range(10))
print(next(squares_gen)) # 0
print(next(squares_gen)) # 1
print(list(squares_gen)) # [4, 9, 16, 25, 36, 49, 64, 81]类与面向对象
class Animal:
def __init__(self, name, sound):
self.name = name
self.sound = sound
def speak(self):
return f"{self.name} says {self.sound}!"
def __repr__(self):
return f"Animal('{self.name}', '{self.sound}')"
class Dog(Animal):
def __init__(self, name):
super().__init__(name, "Woof")
def fetch(self, item):
return f"{self.name} fetches the {item}"
# 使用
dog = Dog("Buddy")
print(dog.speak()) # "Buddy says Woof!"
print(dog.fetch("ball")) # "Buddy fetches the ball"异常处理
# 基础异常处理
try:
result = 10 / 0
except ZeroDivisionError:
print("不能除以零！")
except Exception as e:
print(f"发生错误: {e}")
finally:
print("总是执行")
# 自定义异常
class CustomError(Exception):
def __init__(self, message):
self.message = message
super().__init__(self.message)
def check_value(value):
if value < 0:
raise CustomError("值不能为负数")
return value
try:
check_value(-1)
except CustomError as e:
print(e) # "值不能为负数"上下文管理器
# 使用 with 语句
with open('file.txt', 'w') as f:
f.write("Hello, World!")
# 自定义上下文管理器
class Timer:
def __enter__(self):
import time
self.start = time.time()
return self
def __exit__(self, exc_type, exc_val, exc_tb):
import time
self.end = time.time()
print(f"执行时间: {self.end - self.start:.4f} 秒")
with Timer():
import time
time.sleep(1)小贴士： Python 3.10+ 引入了 match-case 语句（模式匹配），这是一种更强大的条件判断方式。
总结
掌握这些 Python 核心语法将帮助你编写更简洁、高效的代码。建议在实际项目中多加练习，逐步掌握每个特性的使用场景。