Python3 fileoperationtutorial

fileoperationIntroduction

fileoperation is programmingin非常 important 一部分, 它允许我们读取 and 写入data to filein, implementationdata 持久化store. in Pythonin, fileoperation非常 simple 直观, 主要through in 置 open()function来implementation.

Pythonin fileoperation主要including:

• 文本file 读写
• 二进制file 读写
• fileobject method
• file and Table of Contents management
• on under 文management器 (with语句) using

文本file 读写

打开file

usingopen()function打开file, 语法such as under :

open(file, mode='r', encoding=None)

parameter说明:

• file: filepath
• mode: 打开模式, 默认 for 'r' (只读)
• encoding: 编码方式, for 于文本file, 建议指定编码, such as'utf-8'

常用 打开模式:

• 'r': 只读模式 (默认)
• 'w': 写入模式, 会覆盖原 has in 容
• 'a': 追加模式, in file末尾添加 in 容
• 'x': creation模式, creation new file, such as果file已存 in 则报错
• 'r+': 读写模式
• 'w+': 读写模式, 会覆盖原 has in 容
• 'a+': 读写模式, in file末尾添加 in 容

读取file

打开file after , 可以using以 under method读取file in 容:

• read(): 读取整个file
• readline(): 读取一行
• readlines(): 读取所 has 行, 返回list

# 读取整个file
with open('example.txt', 'r', encoding='utf-8') as f:
    content = f.read()
    print(content)

# 逐行读取
with open('example.txt', 'r', encoding='utf-8') as f:
    for line in f:
        print(line.strip())

# 读取所 has 行 to list
with open('example.txt', 'r', encoding='utf-8') as f:
    lines = f.readlines()
    for line in lines:
        print(line.strip())

写入file

打开file after , 可以using以 under method写入file in 容:

• write(): 写入string
• writelines(): 写入stringlist

# 写入file
with open('output.txt', 'w', encoding='utf-8') as f:
    f.write('Hello, World!\n')
    f.write('Welcome to Python file operations.\n')

# 写入 many 行
lines = ['Line 1\n', 'Line 2\n', 'Line 3\n']
with open('output.txt', 'a', encoding='utf-8') as f:
    f.writelines(lines)

fileobject method

常用method

• close(): 关闭file
• flush(): 刷 new 缓冲区, 将 in 容写入file
• tell(): 返回当 before file指针位置
• seek(offset, whence): movefile指针位置
  • offset: 偏移量
  • whence: 起始位置, 0表示file开头, 1表示当 before 位置, 2表示file末尾
• readable(): 判断file is 否 readable
• writable(): 判断file is 否可写
• closed: 判断file is 否已关闭

# file指针operation
with open('example.txt', 'r+', encoding='utf-8') as f:
    # 读取 before 10个字符
    content = f.read(10)
    print(f"First 10 characters: {content}")
    
    # 获取当 before 位置
    position = f.tell()
    print(f"Current position: {position}")
    
    # move to file开头
    f.seek(0)
    print(f"Position after seek(0): {f.tell()}")
    
    # 读取一行
    line = f.readline()
    print(f"First line: {line.strip()}")
    
    # move to file末尾
    f.seek(0, 2)
    print(f"Position at end: {f.tell()}")
    
    # 写入 in 容
    f.write('\nAdded at the end')

二进制file 读写

for 于二进制file (such asgraph片, 音频, 视频etc.) , 需要using二进制模式打开file, 即 in 模式string before 加 on 'b'.

# 读取二进制file
with open('image.jpg', 'rb') as f:
    data = f.read()
    print(f"File size: {len(data)} bytes")

# 写入二进制file
with open('copy_image.jpg', 'wb') as f:
    f.write(data)
    print("Binary file copied successfully")

file and Table of Contents operation

Python os and os.pathmoduleproviding了file and Table of Contents operationfunctions.

osmodule常用function

• os.getcwd(): 获取当 before 工作Table of Contents
• os.chdir(path): 改变当 before 工作Table of Contents
• os.listdir(path): 列出Table of Contentsin file and 子Table of Contents
• os.mkdir(path): creation单级Table of Contents
• os.makedirs(path): creation many 级Table of Contents
• os.remove(path): deletefile
• os.rmdir(path): delete空Table of Contents
• os.removedirs(path): delete many 级空Table of Contents
• os.rename(src, dst): renamefile or Table of Contents
• os.path.exists(path): 判断path is 否存 in
• os.path.isfile(path): 判断 is 否 for file
• os.path.isdir(path): 判断 is 否 for Table of Contents
• os.path.join(path1, path2, ...): 拼接path
• os.path.abspath(path): 获取绝 for path
• os.path.basename(path): 获取file名
• os.path.dirname(path): 获取Table of Contents名

import os
import os.path

# 获取当 before 工作Table of Contents
print(f"Current working directory: {os.getcwd()}")

# 列出Table of Contents in 容
print("\nDirectory contents:")
for item in os.listdir('.'):
    print(item)

# creationTable of Contents
if not os.path.exists('test_dir'):
    os.mkdir('test_dir')
    print("\nDirectory 'test_dir' created")

# creation many 级Table of Contents
if not os.path.exists('test_dir/sub_dir1/sub_dir2'):
    os.makedirs('test_dir/sub_dir1/sub_dir2')
    print("Multi-level directories created")

# checkpath
print("\nPath checks:")
print(f"'test_dir' exists: {os.path.exists('test_dir')}")
print(f"'test_dir' is directory: {os.path.isdir('test_dir')}")
print(f"'example.txt' is file: {os.path.isfile('example.txt')}")

# pathoperation
print("\nPath operations:")
full_path = os.path.join(os.getcwd(), 'test_dir', 'file.txt')
print(f"Full path: {full_path}")
print(f"File name: {os.path.basename(full_path)}")
print(f"Directory name: {os.path.dirname(full_path)}")
print(f"Absolute path: {os.path.abspath('test_dir')}")

# renamefile
try:
    with open('old_name.txt', 'w') as f:
        f.write('Test content')
    os.rename('old_name.txt', 'new_name.txt')
    print("\nFile renamed successfully")
except Exception as e:
    print(f"Error: {e}")

# deletefile and Table of Contents
try:
    if os.path.exists('new_name.txt'):
        os.remove('new_name.txt')
        print("File deleted successfully")
    if os.path.exists('test_dir/sub_dir1/sub_dir2'):
        os.removedirs('test_dir/sub_dir1/sub_dir2')
        print("Directories deleted successfully")
except Exception as e:
    print(f"Error: {e}")

on under 文management器 (with语句)

on under 文management器 is Pythonin一种特殊 object, 它可以 in 进入 and 退出code块时执行specific operation. in fileoperationin, usingwith语句可以自动managementfile 打开 and 关闭, 即使 in operation过程in发生exception, 也能确保file被正确关闭.

# usingwith语句 (推荐) 
with open('example.txt', 'r', encoding='utf-8') as f:
    content = f.read()
    print(content)
# file会自动关闭

# 不usingwith语句 (不推荐) 
f = open('example.txt', 'r', encoding='utf-8')
try:
    content = f.read()
    print(content)
finally:
    f.close()  # 必须手动关闭file

usingwith语句 good 处:

• code更简洁
• 自动processingfile关闭
• 即使发生exception, 也能确保file被正确关闭
• 避免resource泄漏

互动练习

def analyze_file(file_path):
    """
    analysis文本file
    
    Args:
        file_path: filepath
    
    Returns:
        dict: package含行数, 单词数 and 字符数 dictionary
    """
    # implementation你 code
    pass

# testfunction
file_path = 'example.txt'
result = analyze_file(file_path)
print(f"File analysis for {file_path}:")
print(f"Lines: {result['lines']}")
print(f"Words: {result['words']}")
print(f"Characters: {result['characters']}")

import os

def traverse_directory(directory):
    """
    遍历Table of Contents
    
    Args:
        directory: Table of Contentspath
    
    Returns:
        dict: package含fileclass型 and 数量 dictionary
    """
    # implementation你 code
    pass

# testfunction
dir_path = '.'
result = traverse_directory(dir_path)
print(f"Directory traversal for {dir_path}:")
for file_type, count in result.items():
    print(f"{file_type}: {count}")

import datetime

def write_log(log_file, message, log_level='INFO'):
    """
    写入log
    
    Args:
        log_file: logfilepath
        message: logmessage
        log_level: log级别, 默认 for 'INFO'
    """
    # implementation你 code
    pass

# testfunction
log_file = 'app.log'
write_log(log_file, 'Application started')
write_log(log_file, 'User logged in', 'INFO')
write_log(log_file, 'Database connection failed', 'ERROR')
write_log(log_file, 'Application closed', 'INFO')

# 读取并显示log
with open(log_file, 'r') as f:
    print("Log contents:")
    for line in f:
        print(line.strip())