Python 常用基础语法速查。
# 单行注释
"""
多行字符串。
也常被用作多行注释。
"""
'''
也可以使用单引号形式。
'''
Python 变量无需预先声明类型。
name = "Luke"
age = 30
temperature = 25.5
is_active = True
print(name)
print("姓名：", name)
print(f"姓名：{name}，年龄：{age}")
# 字符串
text = "Hello"
# 整数
count = 10
# 浮点数
price = 19.99
# 布尔值
is_valid = True
# 空值
result = None
查看变量类型：
value = 123
print(type(value)) # <class 'int'>
常用类型转换：
number = int("123")
price = float("12.5")
text = str(123)
flag = bool(1)
print(number) # 123
print(price) # 12.5
print(text) # "123"
print(flag) # True
text = "Python"
print(text[0]) # P
print(text[-1]) # n
print(text[0:3]) # Pyt
print(text[2:]) # thon
print(len(text)) # 6
常用操作：
text = " Hello Python "
print(text.strip()) # "Hello Python"
print(text.lower()) # " hello python "
print(text.upper()) # " HELLO PYTHON "
print(text.replace("Python", "World"))
print(text.split()) # ["Hello", "Python"]
print(" - ".join(["A", "B", "C"])) # A - B - C
字符串格式化：
name = "Luke"
score = 95.5
message = f"{name} 的分数是 {score:.1f}"
print(message)
list列表是有序、可修改的集合。
fruits = ["apple", "banana", "orange"]
print(fruits[0]) # apple
print(fruits[-1]) # orange
print(fruits[0:2]) # ["apple", "banana"]
常用操作：
fruits = ["apple", "banana"]
fruits.append("orange") # 末尾添加
fruits.insert(0, "grape") # 指定位置插入
fruits.remove("banana") # 删除指定值
last_item = fruits.pop() # 删除并返回最后一项
fruits.sort() # 原地排序
fruits.reverse() # 原地反转
print(fruits)
遍历列表：
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
print(fruit)
tuple元组与列表类似，但创建后不能修改。
point = (10, 20)
print(point[0]) # 10
print(point[1]) # 20
解包：
x, y = (10, 20)
print(x) # 10
print(y) # 20
单元素元组需要保留逗号：
single_value = (1,)
dict字典以“键：值”的方式存储数据。
user = {
"name": "Luke",
"age": 30,
"department": "Digital Promotion"
}
print(user["name"]) # Luke
print(user.get("age")) # 30
print(user.get("email")) # None
print(user.get("email", "")) # ""
新增、修改和删除：
user = {"name": "Luke"}
user["age"] = 30
user["name"] = "Peter"
del user["age"]
遍历字典：
user = {
"name": "Luke",
"age": 30
}
for key in user:
print(key, user[key])
for key, value in user.items():
print(f"{key}: {value}")
set集合中的元素唯一且无固定顺序。
numbers = {1, 2, 3, 3, 3}
print(numbers) # {1, 2, 3}
常用操作：
numbers = {1, 2, 3}
numbers.add(4)
numbers.remove(2)
numbers.discard(999) # 元素不存在时不会报错
print(numbers)
集合运算：
a = {1, 2, 3}
b = {3, 4, 5}
print(a | b) # 并集：{1, 2, 3, 4, 5}
print(a & b) # 交集：{3}
print(a - b) # 差集：{1, 2}
score = 85
if score >= 90:
print("优秀")
elif score >= 60:
print("合格")
else:
print("不合格")
多个条件：
age = 25
has_ticket = True
if age >= 18 and has_ticket:
print("允许进入")
if age < 18 or not has_ticket:
print("不允许进入")
常用比较运算符：
a == b # 等于
a != b # 不等于
a > b # 大于
a >= b # 大于等于
a < b # 小于
a <= b # 小于等于
判断成员是否存在：
fruits = ["apple", "banana"]
if "apple" in fruits:
print("存在 apple")
if "orange" not in fruits:
print("不存在 orange")
for 循环for i in range(5):
print(i)
输出：
0
1
2
3
4
range() 常见用法：
range(5) # 0 到 4
range(1, 5) # 1 到 4
range(0, 10, 2) # 0、2、4、6、8
同时获取索引和值：
fruits = ["apple", "banana", "orange"]
for index, fruit in enumerate(fruits):
print(index, fruit)
while 循环count = 0
while count < 3:
print(count)
count += 1
break、continue 与 passfor i in range(10):
if i == 3:
continue # 跳过本次循环
if i == 7:
break # 结束整个循环
print(i)
if True:
pass # 暂时不执行任何操作
定义函数：
def greet(name):
print(f"你好，{name}！")
greet("Luke")
带返回值的函数：
def add(a, b):
return a + b
result = add(10, 20)
print(result) # 30
默认参数：
def greet(name, greeting="你好"):
return f"{greeting}，{name}！"
print(greet("Luke"))
print(greet("Luke", "Good morning"))
关键字参数：
def create_user(name, age, department):
return {
"name": name,
"age": age,
"department": department
}
user = create_user(
name="Luke",
age=30,
department="Digital Promotion"
)
可变参数：
def total(*numbers):
return sum(numbers)
print(total(1, 2, 3, 4))
可变关键字参数：
def print_info(**kwargs):
for key, value in kwargs.items():
print(f"{key}: {value}")
print_info(name="Luke", age=30)
列表推导式：
numbers = [1, 2, 3, 4, 5]
squares = [number ** 2 for number in numbers]
print(squares) # [1, 4, 9, 16, 25]
带条件的列表推导式：
even_numbers = [number for number in numbers if number % 2 == 0]
print(even_numbers) # [2, 4]
字典推导式：
scores = {
"Alice": 90,
"Bob": 85,
"Chris": 92
}
score_levels = {
name: "Pass"
for name, score in scores.items()
if score >= 60
}
print(score_levels)
try:
number = int(input("请输入数字："))
print(100 / number)
except ValueError:
print("输入内容不是有效数字")
except ZeroDivisionError:
print("除数不能为 0")
finally:
print("处理结束")
主动抛出异常：
age = -1
if age < 0:
raise ValueError("年龄不能小于 0")
导入整个模块：
import math
print(math.sqrt(16))
导入指定内容：
from datetime import datetime
now = datetime.now()
print(now)
使用别名：
import pandas as pd
读取文本文件：
with open("example.txt", "r", encoding="utf-8") as file:
content = file.read()
print(content)
逐行读取：
with open("example.txt", "r", encoding="utf-8") as file:
for line in file:
print(line.strip())
写入文本文件：
with open("example.txt", "w", encoding="utf-8") as file:
file.write("Hello, Python!\n")
追加文本内容：
with open("example.txt", "a", encoding="utf-8") as file:
file.write("追加一行内容\n")
numbers = [3, 1, 4, 1, 5]
print(len(numbers)) # 长度
print(sum(numbers)) # 求和
print(min(numbers)) # 最小值
print(max(numbers)) # 最大值
print(sorted(numbers)) # 返回排序后的新列表
print(list(reversed(numbers))) # 反转
for index, value in enumerate(["a", "b", "c"]):
print(index, value)
for name, score in zip(["Alice", "Bob"], [90, 85]):
print(name, score)
| 对象 | 推荐格式 | 示例 |
|---|---|---|
| 变量、函数 | snake_case |
user_name、get_data() |
| 类 | PascalCase |
UserService |
| 常量 | UPPER_CASE |
MAX_RETRY_COUNT |
| 私有成员 | 前置单下划线 | _internal_value |
| 特殊方法 | 双下划线 | __init__、__str__ |
def check_temperature(temperature, min_temp=300, max_temp=340):
"""判断温度是否在合格范围内。"""
if min_temp <= temperature <= max_temp:
return "OK"
return "NG"
temperatures = [298.5, 315.2, 342.0]
for temperature in temperatures:
result = check_temperature(temperature)
print(f"温度：{temperature:.1f}℃，结果：{result}")
输出示例：
温度：298.5℃，结果：NG
温度：315.2℃，结果：OK
温度：342.0℃，结果：NG
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