第11讲 · 读取与写入文本文件

读取与写入文本文件

读取已有内容，覆盖或追加写入，并打开文件检查最终结果。

1读取文件中的已有内容

2覆盖或追加写入新内容

3打开文件检查最终结果

用 open() 选择读写模式

1r：读取已有文件

2w：覆盖写入文件

3a：在文件末尾追加内容

语法拆解

open(path, "r", encoding="utf-8"): 读取文本
open(path, "w", encoding="utf-8"): 覆盖写入
open(path, "a", encoding="utf-8"): 追加写入

用 read() 读取完整内容

l11_read_all.py

with open(path, "r", encoding="utf-8") as file:
    content = file.read()
print(content)

open(path, "r", encoding="utf-8"): 以只读方式打开
content = file.read(): 读取全部剩余内容

1r模式不会修改文件

2read返回一个完整字符串

3短文本可以一次读取

用 readline() 读取一行

l11_readline.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = prepare_text("class_notes.txt", "第一行\n第二行\n第三行\n")
with open(path, "r", encoding="utf-8") as file:
    first_line = file.readline()
    second_line = file.readline()
print(repr(first_line))
print(repr(second_line))

line = file.readline(): 读取当前位置的一行
repr(line): 观察换行符

1每次只读取一行

2返回值通常带有换行符

3再次调用会继续读取下一行

用 for 逐行读取

l11_iterate_lines.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = prepare_text("class_notes.txt", "读取文件\n写入文件\n检查结果\n")
with open(path, "r", encoding="utf-8") as file:
    for number, line in enumerate(file, 1):
        print(number, line.rstrip("\n"))

for line in file:: 逐行读取文件
line.rstrip('\n'): 去掉行尾换行

1文件对象可以直接遍历

2每轮得到当前一行

3适合较长文本

用 w 模式覆盖写入

l11_write_new.py

with open(path, "w", encoding="utf-8") as file:
    file.write("今天学习文件写入\n")
print("写入完成")

open(path, "w", encoding="utf-8"): 覆盖方式打开
file.write("今天学习文件写入\n"): 写入新内容

1w会先清空旧内容

2write写入一个字符串

3写入内容需要自己添加换行符

打开文件检查写入结果

l11_check_write.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = os.path.join(WORKSPACE, "class_notes.txt")
with open(path, "w", encoding="utf-8") as file:
    file.write("Python可以修改文本文件\n")
with open(path, "r", encoding="utf-8") as file:
    saved = file.read()
print("重新读取：", saved, end="")

file.write(content): 保存内容
saved = file.read(): 重新读取结果

1先完成写入

2再用r模式重新读取

3打开文件做可视化核对

用 a 模式追加内容

l11_append.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = prepare_text("class_notes.txt", "原有笔记\n")
with open(path, "a", encoding="utf-8") as file:
    file.write("追加笔记\n")
print("追加完成：", path)

open(path, "a", encoding="utf-8"): 追加方式打开
file.write("追加笔记\n"): 写在末尾

1a保留原内容

2新文字写在文件末尾

3追加多行时显式写入换行符

比较 w 与 a 的文件变化

l11_compare_modes.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = prepare_text("mode_demo.txt", "初始内容\n")
with open(path, "w", encoding="utf-8") as file:
    file.write("覆盖后的内容\n")
with open(path, "a", encoding="utf-8") as file:
    file.write("追加内容\n")
with open(path, "r", encoding="utf-8") as file:
    print(file.read(), end="")

w → replace: 覆盖原文件
a → append: 保留并追加

1w：替换整个文件内容

2a：在现有末尾继续写

3选择模式前先确认是否保留旧内容

用 with 自动关闭文件

l11_with_context.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = os.path.join(WORKSPACE, "class_notes.txt")
with open(path, "w", encoding="utf-8") as file:
    file.write("with会自动关闭文件\n")
    print("代码块内已关闭：", file.closed)
print("代码块外已关闭：", file.closed)

with open(...) as file:: 创建文件上下文
file.closed: 检查是否已经关闭

1进入with后文件处于打开状态

2离开缩进块后自动关闭

3读写代码更完整可靠

完成课堂笔记文件

先读取原始标题 · 用w写入整理后的内容 · 用a追加本节收获 · 打开文件完成验收

course_notes.py

with open(path, "w", encoding="utf-8") as file:
    file.write(title + "\n- 文件读取\n")
with open(path, "a", encoding="utf-8") as file:
    file.write("- 文件写入\n")

verify_course_notes.py

import os

WORKSPACE = "/tmp/lesson11_workspace"
os.makedirs(WORKSPACE, exist_ok=True)

def prepare_text(filename, content):
    path = os.path.join(WORKSPACE, filename)
    with open(path, "w", encoding="utf-8") as fixture:
        fixture.write(content)
    return path

path = os.path.join(WORKSPACE, "course_notes.txt")
expected = "Python课堂笔记\n- 文件读取\n- 文件写入\n"
with open(path, "w", encoding="utf-8") as file:
    file.write(expected)
with open(path, "r", encoding="utf-8") as file:
    actual = file.read()
print("内容正确：", actual == expected)
print("文件已关闭：", file.closed)

复盘文件读写流程

1定位文件：确认工作目录与目标路径

2读取文件：r配合read、readline或for

3写入文件：w覆盖，a追加

4关闭文件：统一使用with

5验收结果：重新读取并打开文件核对

语法拆解

open → read: 打开并读取
open → write: 覆盖或追加
reopen → inspect: 重新打开并验收