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python学习笔记20-文件操作

1. 文件是什么？

文件是以计算机硬盘为载体存储在计算机上的信息集合，文件可以是文本文档、图片、程序等等。计算机文件基本上分为两种：

  • 二进制文件：没有统一字符编码（图片/音频/视频/可执行文件等）
  • 纯文本文件：有统一编码（可视为存储在磁盘上的长字符串）

常见纯文本编码：ASCII、ISO-8859-1、GB2312、GBK、UTF-8、UTF-16 等。实践中处理文本文件通常选 UTF-8。

典型 I/O 流程：打开 → 读/写 → 刷新/移动指针 → 关闭

2. open() 打开文件与关闭文件

2.1 open 基本语法与参数

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file_object = open(
    file_path,
    mode='r',
    encoding=None,
    errors=None,
    newline=None,
    closefd=True,
    opener=None
)
  • file_path：文件路径（相对/绝对）
  • mode：读写模式（见下一节）
  • encoding：文本编码（建议显式指定 utf-8）
  • errors：编码/解码错误处理策略
  • newline：换行符处理（写 CSV 常用 newline=''）
  • closefd/opener：高级参数，通常不需要

2.2 推荐用法：with 自动关闭

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file_path = 'example.txt'
with open(file_path, 'r', encoding='utf-8') as file:
    file_content = file.read()
    print(file_content)

2.3 手动关闭：close()

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file_path = 'example.txt'
file = open(file_path, 'r', encoding='utf-8')
try:
    file_content = file.read()
    print(file_content)
finally:
    file.close()

3. 文件读写模式

模式含义
r只读（默认，文件必须存在，不存在抛异常）
w只写，写之前清空文件内容；文件不存在则创建
a追加写，文件指针在末尾；文件不存在则创建
r+可读可写（文件必须存在）
w+读写（覆盖）；文件不存在则创建
a+读写（追加）；文件不存在则创建
rb二进制只读
wb二进制只写（覆盖）
ab二进制追加
rb+二进制可读可写
wb+二进制读写（覆盖）
ab+二进制读写（追加）

4. 文件对象常用方法

分类方法说明示例
打开文件open(file, mode='r', ...)返回文件对象file = open('example.txt', 'r')
读取read(size=-1)读取整个文件或指定大小content = file.read()
读取readline(size=-1)读取一行line = file.readline()
读取readlines(hint=-1)读取全部行 → 列表lines = file.readlines()
写入write(string)写入字符串/bytesfile.write('Hello\\n')
写入writelines(lines)写入多行（不自动加换行）file.writelines(['a\\n','b\\n'])
指针seek(offset, whence=0)移动文件指针file.seek(0)
指针tell()返回当前指针pos = file.tell()
缓冲flush()刷新缓冲区file.flush()
关闭close()关闭文件file.close()
上下文with open(...) as f:自动管理打开/关闭with open(...) as f: ...
二进制open(file, 'rb')二进制读with open('a.png','rb') as f:

5. 读取文件（read / readline / readlines）

5.1 read：读取全部内容

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file_path = 'example.txt'
with open(file_path, 'r', encoding='utf-8') as file:
    data = file.read()
    print(data)

5.2 readline：逐行读取

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with open('file.txt', 'r', encoding='utf-8') as file:
    line = file.readline()

逐行读取整个文件：

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with open('file.txt', 'r', encoding='utf-8') as file:
    line = file.readline()
    while line != '':
        print(line.strip())
        line = file.readline()

5.3 readlines：一次性读取全部行

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with open('file.txt', 'r', encoding='utf-8') as file:
    lines = file.readlines()
print(lines)
print(lines[0].strip())

5.4 readlines vs readline

  • readlines()：一次性读取所有行 → 列表，适合小文件
  • readline()：一次读取一行，适合大文件逐行处理，内存占用更小

5.5 大文件读取建议

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with open('big.txt', 'r', encoding='utf-8') as f:
    for line in f:
        process(line)

with open('big.bin', 'rb') as f:
    for chunk in iter(lambda: f.read(1024 * 1024), b''):
        process(chunk)

6. 写入文件（write）

6.1 写入文本文件

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file_path = 'example.txt'
with open(file_path, 'w', encoding='utf-8') as file:
    file.write("Hello, this is some data.")

6.2 写入 CSV 文件

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import csv

csv_file_path = 'example.csv'
data = [
    ['Name', 'Age', 'Occupation'],
    ['John Doe', 30, 'Engineer'],
    ['Jane Smith', 25, 'Designer']
]

with open(csv_file_path, 'w', newline='', encoding='utf-8') as csvfile:
    csv_writer = csv.writer(csvfile)
    csv_writer.writerows(data)

6.3 写入 JSON 文件

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import json

json_file_path = 'example.json'
data = {"name": "John Doe", "age": 30, "occupation": "Engineer"}

with open(json_file_path, 'w', encoding='utf-8') as jsonfile:
    json.dump(data, jsonfile, ensure_ascii=False, indent=2)

6.4 写入数据库（以 sqlite3 为例）

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import sqlite3

conn = sqlite3.connect('example.db')
cursor = conn.cursor()
cursor.execute('CREATE TABLE IF NOT EXISTS users (name TEXT, age INTEGER, occupation TEXT)')
cursor.execute(
    "INSERT INTO users (name, age, occupation) VALUES (?, ?, ?)",
    ('John Doe', 30, 'Engineer')
)
conn.commit()
conn.close()

7. 从文件/数据库读取数据（含示例）

7.1 读取 CSV

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import csv

csv_file_path = 'example.csv'
with open(csv_file_path, 'r', encoding='utf-8') as csvfile:
    csv_reader = csv.reader(csvfile)
    for row in csv_reader:
        print(row)

7.2 读取 JSON

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import json

json_file_path = 'example.json'
with open(json_file_path, 'r', encoding='utf-8') as jsonfile:
    data = json.load(jsonfile)
    print(data)

7.3 从数据库读取（sqlite3）

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import sqlite3

conn = sqlite3.connect('example.db')
cursor = conn.cursor()
cursor.execute("SELECT * FROM users")
rows = cursor.fetchall()
for row in rows:
    print(row)
conn.close()

8. 二进制文件操作

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with open('example.bin', 'wb') as file:
    file.write(b'\x00\x01\x02\x03\x04')

with open('example.bin', 'rb') as file:
    content = file.read()
    print(content)

9. 文件指针与缓冲（seek / tell / flush）

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with open('example.txt', 'r+', encoding='utf-8') as file:
    content = file.read(5)
    print(content)
    file.seek(0)
    file.write('Hi ')
    file.flush()
    position = file.tell()
    print(position)
  • seek(offset, whence=0)：改变指针位置，whence=0/1/2 对应 开头/当前位置/末尾
  • tell()：返回指针当前位置
  • flush()：把缓冲区数据立即写入磁盘

10. 使用 os 与 pathlib 进行文件/目录操作

10.1 os 常用

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import os

os.makedirs('new_directory', exist_ok=True)
os.remove('example.txt')
os.rename('old_name.txt', 'new_name.txt')
print(os.listdir('.'))

10.2 pathlib 常用

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from pathlib import Path

path = Path('example.txt')
if path.exists():
    print('File exists.')

Path('new_directory').mkdir(parents=True, exist_ok=True)
content = path.read_text(encoding='utf-8')
print(content)

11. 文件相关管理操作（重命名/删除/创建/当前目录）

11.1 文件重命名（含异常处理）

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import os

directory = 'path_to_directory'
files = os.listdir(directory)

try:
    for file_name in files:
        full_path = os.path.join(directory, file_name)
        if os.path.isfile(full_path):
            new_filename = 'new_name'
            os.rename(full_path, os.path.join(directory, new_filename))
except OSError as e:
    print(f'Error occurred: {e}')

高级：正则批量生成新名称：

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import os
import re

directory = 'path_to_directory'
files = os.listdir(directory)

for file_name in files:
    src = os.path.join(directory, file_name)
    if os.path.isfile(src):
        new_filename = re.sub(r'\d+', 'new_prefix', file_name)
        dst = os.path.join(directory, new_filename)
        try:
            os.rename(src, dst)
        except OSError as e:
            print(f'Error renaming {file_name}: {e}')

11.2 删除文件

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import os

file_path = 'path_to_file'
if os.path.isfile(file_path):
    try:
        os.remove(file_path)
        print(f'File {file_path} deleted successfully.')
    except OSError as e:
        print(f'Error occurred: {e}')

11.3 创建文件

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import os

file_path = 'path_to_file'
if not os.path.exists(file_path):
    try:
        with open(file_path, 'w', encoding='utf-8') as f:
            pass
    except IOError as e:
        print(f'Error occurred: {e}')

11.4 获取当前目录

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import os

current_directory = os.getcwd()
print(f'Current directory is: {current_directory}')

12. 示例脚本

12.1 目录.txt 自动清洗

规则：

  • 二级标题行前空 4 个格子（一级标题不加）
  • “章/节” 后加空格
  • 页码前加 =>
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import os
import re

desktop_path = os.path.join(os.path.expanduser("~"), "Desktop")
file_path = os.path.join(desktop_path, "目录.txt")

with open(file_path, 'r', encoding='utf-8') as file:
    lines = file.readlines()

modified_lines = []
for line in lines:
    line = line.replace(" ", "")
    if len(line) == 1:
        continue

    line = re.sub(r'(章|节)(?![ ])', r'\1 ', line)
    line = re.sub(r'(\.\d)', r'\1 ', line)

    if '章' not in line:
        line = ' ' * 4 + line

    line = re.sub(r'\(([\d\s]+)\)', r'\1', line)
    line = re.sub(r'（([^）]+)）', r'\1', line)

    if '=>' not in line:
        line = re.sub(r'(\d+)$', r'=>\1', line)

    line = re.sub(r'([\u4e00-\u9fff]+)[^\w\s]+=>', r'\1=>', line)
    modified_lines.append(line)

with open(file_path, 'w', encoding='utf-8') as file:
    file.writelines(modified_lines)

with open(file_path, 'r', encoding='utf-8') as file:
    print(file.read())

12.2 批量修改文件夹下文件命名（补齐前缀）

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import os

directory_path = r'目标文件夹绝对路径'
prefix = '00000000000'

files = os.listdir(directory_path)
for file_name in files:
    file_path = os.path.join(directory_path, file_name)

    if file_name.lower().endswith(('.png', '.jpg', '.jpeg', '.gif')) and '_' in file_name:
        parts = file_name.split('_')
        if parts[0] != prefix:
            new_file_name = prefix + '_' + '_'.join(parts[1:])
            new_file_path = os.path.join(directory_path, new_file_name)
            os.rename(file_path, new_file_path)
            print(f'Renamed: {file_name} -> {new_file_name}')

12.3 检测同级目录下是否存在同名文件夹（前 5 位重复）

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import os

directory_path = r'目标路径'
folders = [
    folder
    for folder in os.listdir(directory_path)
    if os.path.isdir(os.path.join(directory_path, folder))
]

same_prefix_folders = {}
for folder in folders:
    prefix = folder[:5]
    if prefix in same_prefix_folders:
        same_prefix_folders[prefix].append(folder)
    else:
        same_prefix_folders[prefix] = [folder]

for prefix, items in same_prefix_folders.items():
    if len(items) > 1:
        print(f\"前5位为 '{prefix}' 的文件夹有以下重复命名：\")
        print(', '.join(items))

13. 安全与健壮性

  • 文本文件尽量显式指定 encoding='utf-8'
  • 读取/写入时根据需要设置 errors='ignore'/'replace'
  • 写 CSV 建议 newline=''
  • 原子写入：临时文件写完再替换，避免半成品
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from pathlib import Path
import os
import tempfile

data = 'content'
target = Path('safe.txt')
with tempfile.NamedTemporaryFile('w', delete=False, encoding='utf-8') as tmp:
    tmp.write(data)
    tmp_path = Path(tmp.name)
os.replace(tmp_path, target)

14. 小结

  • 基础：with open(path, 'r/w/a', encoding='utf-8')
  • 大文件：优先逐行/分块，不要一次 read() 全部
  • CSV：写入 newline=''
  • JSON：写入 ensure_ascii=False + indent
  • 二进制：加 b（rb/wb/ab）
  • 目录/路径：pathlib.Path 更顺手
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