一、学习目标
掌握文本文件的读写操作（打开、读取、写入、关闭）
理解with语句与上下文管理器的使用
学习CSV和JSON文件的读写
掌握异常处理机制（try-except-else-finally）
学会自定义异常类
能够编写健壮的文件处理程序
二、学习内容
- 文件操作基础
打开文件：open(filename, mode)
mode：'r'读、'w'写（覆盖）、'a'追加、'r+'读写
encoding：指定编码（如utf-8）
关闭文件：file.close()
读取：read()、readline()、readlines()
写入：write()、writelines()
python
写文件
file = open("test.txt", "w", encoding="utf-8")
file.write("Hello, Python!\n")
file.write("这是第一行\n第二行")
file.close()
读文件
file = open("test.txt", "r", encoding="utf-8")
content = file.read()
print(content)
file.close()
2. 使用with语句（推荐）
自动管理文件关闭，即使发生异常也能正确关闭
python
写入
with open("test.txt", "w", encoding="utf-8") as f:
f.write("使用with写入\n")
读取
with open("test.txt", "r", encoding="utf-8") as f:
for line in f: # 逐行读取（高效）
print(line, end="")
3. 文件读取方法对比
python
with open("test.txt", "r", encoding="utf-8") as f:
# 1. 读取全部内容为字符串
data = f.read()
# 2. 读取一行
line = f.readline()# 3. 读取所有行到列表
lines = f.readlines()# 4. 迭代器方式（推荐大文件）
for line in f:process(line)
- CSV文件处理
python
import csv
写入CSV
data = [
["姓名", "年龄", "城市"],
["小明", 18, "北京"],
["小红", 20, "上海"]
]
with open("students.csv", "w", newline="", encoding="utf-8") as f:
writer = csv.writer(f)
writer.writerows(data)
读取CSV
with open("students.csv", "r", encoding="utf-8") as f:
reader = csv.reader(f)
for row in reader:
print(row)
使用DictWriter/DictReader（以字典形式操作）
with open("students.csv", "r", encoding="utf-8") as f:
reader = csv.DictReader(f)
for row in reader:
print(row["姓名"], row["年龄"])
5. JSON文件处理
python
import json
Python对象 -> JSON字符串
data = {
"name": "小明",
"age": 18,
"scores": [85, 92, 78],
"address": {"city": "北京", "district": "海淀"}
}
写入JSON文件
with open("data.json", "w", encoding="utf-8") as f:
json.dump(data, f, ensure_ascii=False, indent=4)
读取JSON文件
with open("data.json", "r", encoding="utf-8") as f:
loaded_data = json.load(f)
print(loaded_data)
JSON字符串转换
json_str = json.dumps(data, ensure_ascii=False)
print(json_str)
6. 异常处理基础
try-except：捕获异常
else：无异常时执行
finally：无论是否异常都执行
python
try:
num = int(input("请输入一个数字："))
result = 10 / num
except ValueError:
print("输入的不是有效数字")
except ZeroDivisionError:
print("不能除以0")
except Exception as e:
print(f"发生未知错误：{e}")
else:
print(f"结果是：{result}")
finally:
print("程序结束")
7. 捕获多个异常
python
try:
file = open("nonexist.txt")
content = file.read()
num = int(content)
except (FileNotFoundError, PermissionError):
print("文件不存在或无法访问")
except ValueError:
print("文件内容不是数字")
8. 抛出异常
python
def divide(a, b):
if b == 0:
raise ValueError("除数不能为0")
return a / b
try:
result = divide(10, 0)
except ValueError as e:
print(f"错误：{e}")
9. 自定义异常
python
class InvalidAgeError(Exception):
"""自定义异常：年龄无效"""
pass
def set_age(age):
if age < 0 or age > 150:
raise InvalidAgeError(f"年龄{age}超出范围")
print(f"年龄设置为{age}")
try:
set_age(200)
except InvalidAgeError as e:
print(f"年龄设置失败：{e}")
10. 结合文件操作与异常处理
python
def read_safe(filename):
try:
with open(filename, "r", encoding="utf-8") as f:
return f.read()
except FileNotFoundError:
print(f"文件{filename}不存在")
return None
except PermissionError:
print("没有读取权限")
return None
except Exception as e:
print(f"读取文件时发生错误：{e}")
return None