09|文件操作与异常处理

文件操作与异常处理

对应教学日历：讲次 8-9

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一、文件打开与关闭

打开文件

handle = open("D:\\exam\\test.txt", 'r')     # 指定路径
handle = open("test.txt", 'r')                # 当前目录

关闭文件

handle.close()

with 语句（推荐）

with open("test.txt", "r", encoding="utf-8") as fobj:
    content = fobj.read()
# 自动关闭文件

打开模式

模式	说明
"r"	只读（默认）
"w"	写入（覆盖原文件）
"a"	追加写入
"r+"	读写
"w+"	写读（覆盖）
"a+"	追加读写

二、文件读操作

read() — 读取整个文件

with open("english.txt", "r", encoding="utf-8") as fobj:
    paper = fobj.read()

readline() — 读取一行

with open("data.txt", "r") as fobj:
    line = fobj.readline()

readlines() — 读取所有行到列表

with open("data.csv", "r") as fobj:
    lines = fobj.readlines()

直接遍历文件（推荐）

with open("data.csv", "r") as fobj:
    for line in fobj:
        line = line.strip()
        print(line)

三、文件写操作

write() — 写入字符串

with open("new.txt", 'w') as handle:
    handle.write("Hello World\n")

writelines() — 写入字符串列表

string = ["hello\n", "world\n"]
with open("new.txt", 'w') as handle:
    handle.writelines(string)

四、CSV文件处理

读取CSV数据

lab = []
with open("data.csv", "r") as fobj:
    for i in fobj:
        i = i.strip()
        i = float(i)
        lab.append(i)
print("最高值为：{:.2f}".format(max(lab)))

按列读取CSV

with open("student.csv", "r") as fobj:
    for i in fobj:
        if i[:2] == "学号":    # 跳过表头
            continue
        info = i.strip().split(",")
        print(info[1])         # 第2列（姓名）

统计CSV数据

count = 0
total = 0
name = input("请输入大类名称：")
with open("competition.csv", "r") as fobj:
    for eachLine in fobj:
        if eachLine[:4] == "作品编号":
            continue
        total = total + 1
        line = eachLine.split(",")
        if line[1] == name:
            count = count + 1
if count != 0:
    print("该大类参赛作品总共为：{}".format(count))
    print("占比为：{:.1f}".format(count / total))

五、异常处理

try:
    <语句块1>
except <异常类型>:
    <语句块2>
else:
    <语句块3>      # 无异常时执行
finally:
    <语句块4>       # 总是执行

除数为零错误

try:
    num1 = int(input("The first number:"))
    num2 = int(input("The second number:"))
    num3 = num1 / num2
    print(num3)
except ZeroDivisionError:
    print("除数为零错误")

文件不存在错误

try:
    with open("二十大报告.txt", "r", encoding='utf-8') as fobj:
        paper = fobj.read()
        print(paper)
except FileNotFoundError:
    print("文件不存在")

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作业示例

文章单词替换并保存

with open("english.txt", 'r') as fobj:
    paper = fobj.read()
content = paper.replace("mouse", "bird")
with open("new.txt", 'w') as handle:
    handle.write(content + '\n')

批量手机号码加密

aList = []
with open('ph.txt', 'r') as fobj:
    for number in fobj:
        new = number[:3] + "****" + number[7:]
        aList.append(new)
with open('result.txt', 'w') as fobj:
    fobj.writelines(aList)

学生成绩处理

scores = []
with open("myscore.txt", "r", encoding="utf-8") as fobj:
    for eachLine in fobj:
        if eachLine[:2] == "姓名":
            continue
        line = eachLine.split()
        scores.append(int(line[1]))
ave = sum(scores) / len(scores)
print(f"The average score of English is {ave:.1f}")

随机点名程序

import time
import random
count = int(input("请输入随机点名人数："))
namelist = []
with open("student.csv", "r") as fobj:
    for i in fobj:
        if i[:2] == "学号":
            continue
        info = i.strip().split(",")
        namelist.append(info[1])
result = random.sample(namelist, count)
time.sleep(1)
for i in result:
    print("{}请回答问题".format(i))

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作业重点

• with open() 自动关闭文件，推荐使用
• read() 读全部，readline() 读一行，readlines() 读所有行到列表
• write() 不自动换行，需要手动加 \n
• writelines() 写入字符串列表，不自动加换行符
• CSV处理：strip() 去换行符，split(",") 按逗号分割
• 跳过表头：if line[:2] == "姓名": continue
• try-except 捕获异常，finally 总是执行
• FileNotFoundError 文件不存在，ZeroDivisionError 除零