文件读写操作¶
问题124：如何打开和关闭文件？¶
# 1. 基本文件操作
file = open("example.txt", "r", encoding="utf-8")
content = file.read()
file.close()
# 2. 使用with语句（推荐）
with open("example.txt", "r", encoding="utf-8") as file:
content = file.read()
# 文件会自动关闭
# 3. 文件模式
# "r" - 读取模式（默认）
# "w" - 写入模式（覆盖）
# "a" - 追加模式
# "x" - 创建模式（文件不存在时创建）
# "b" - 二进制模式
# "t" - 文本模式（默认）
问题125：如何读取文件内容？¶
# 1. 读取整个文件
with open("example.txt", "r", encoding="utf-8") as file:
content = file.read()
print(content)
# 2. 按行读取
with open("example.txt", "r", encoding="utf-8") as file:
lines = file.readlines()
for line in lines:
print(line.strip())
# 3. 逐行读取
with open("example.txt", "r", encoding="utf-8") as file:
for line in file:
print(line.strip())
# 4. 读取指定字符数
with open("example.txt", "r", encoding="utf-8") as file:
chunk = file.read(100) # 读取100个字符
print(chunk)
问题126：如何写入文件内容？¶
# 1. 写入文本
with open("output.txt", "w", encoding="utf-8") as file:
file.write("Hello, World!")
file.write("\n这是第二行")
# 2. 写入多行
lines = ["第一行", "第二行", "第三行"]
with open("output.txt", "w", encoding="utf-8") as file:
file.writelines(line + "\n" for line in lines)
# 3. 追加内容
with open("output.txt", "a", encoding="utf-8") as file:
file.write("\n这是追加的内容")
# 4. 使用print函数写入
with open("output.txt", "w", encoding="utf-8") as file:
print("Hello, World!", file=file)
print("这是第二行", file=file)
问题127：如何处理文件异常？¶
import os
# 1. 检查文件是否存在
def read_file_safely(filename):
if not os.path.exists(filename):
print(f"文件 {filename} 不存在")
return None
try:
with open(filename, "r", encoding="utf-8") as file:
return file.read()
except FileNotFoundError:
print(f"文件 {filename} 未找到")
return None
except PermissionError:
print(f"没有权限访问文件 {filename}")
return None
except UnicodeDecodeError:
print(f"文件 {filename} 编码错误")
return None
except Exception as e:
print(f"读取文件时出错: {e}")
return None
# 2. 使用try-except处理文件操作
def copy_file(source, destination):
try:
with open(source, "r", encoding="utf-8") as src:
content = src.read()
with open(destination, "w", encoding="utf-8") as dst:
dst.write(content)
print(f"文件复制成功: {source} -> {destination}")
except FileNotFoundError:
print(f"源文件 {source} 不存在")
except PermissionError:
print(f"没有权限访问文件")
except Exception as e:
print(f"复制文件时出错: {e}")
问题128：如何处理二进制文件？¶
# 1. 读取二进制文件
def read_binary_file(filename):
try:
with open(filename, "rb") as file:
data = file.read()
return data
except FileNotFoundError:
print(f"文件 {filename} 不存在")
return None
# 2. 写入二进制文件
def write_binary_file(filename, data):
try:
with open(filename, "wb") as file:
file.write(data)
print(f"二进制文件写入成功: {filename}")
except Exception as e:
print(f"写入二进制文件时出错: {e}")
# 3. 复制二进制文件
def copy_binary_file(source, destination):
try:
with open(source, "rb") as src:
with open(destination, "wb") as dst:
while True:
chunk = src.read(1024) # 每次读取1KB
if not chunk:
break
dst.write(chunk)
print(f"二进制文件复制成功: {source} -> {destination}")
except Exception as e:
print(f"复制二进制文件时出错: {e}")
问题129：如何使用pathlib模块处理文件路径？¶
from pathlib import Path
# 1. 创建Path对象
file_path = Path("example.txt")
directory_path = Path("documents")
# 2. 检查路径
print(file_path.exists()) # 检查文件是否存在
print(file_path.is_file()) # 检查是否为文件
print(directory_path.is_dir()) # 检查是否为目录
# 3. 获取路径信息
print(file_path.name) # 文件名
print(file_path.stem) # 文件名（不含扩展名）
print(file_path.suffix) # 文件扩展名
print(file_path.parent) # 父目录
print(file_path.absolute()) # 绝对路径
# 4. 使用pathlib读写文件
def read_file_with_pathlib(filename):
file_path = Path(filename)
if file_path.exists():
return file_path.read_text(encoding="utf-8")
return None
def write_file_with_pathlib(filename, content):
file_path = Path(filename)
file_path.write_text(content, encoding="utf-8")
print(f"文件写入成功: {filename}")
# 5. 创建目录
def create_directory(dirname):
dir_path = Path(dirname)
dir_path.mkdir(exist_ok=True)
print(f"目录创建成功: {dirname}")
问题130：如何处理CSV文件？¶
import csv
# 1. 读取CSV文件
def read_csv_file(filename):
data = []
try:
with open(filename, "r", encoding="utf-8") as file:
reader = csv.reader(file)
for row in reader:
data.append(row)
return data
except FileNotFoundError:
print(f"文件 {filename} 不存在")
return []
# 2. 写入CSV文件
def write_csv_file(filename, data):
try:
with open(filename, "w", encoding="utf-8", newline="") as file:
writer = csv.writer(file)
writer.writerows(data)
print(f"CSV文件写入成功: {filename}")
except Exception as e:
print(f"写入CSV文件时出错: {e}")
# 3. 使用字典读写CSV
def read_csv_as_dict(filename):
data = []
try:
with open(filename, "r", encoding="utf-8") as file:
reader = csv.DictReader(file)
for row in reader:
data.append(row)
return data
except FileNotFoundError:
print(f"文件 {filename} 不存在")
return []
def write_csv_from_dict(filename, data, fieldnames):
try:
with open(filename, "w", encoding="utf-8", newline="") as file:
writer = csv.DictWriter(file, fieldnames=fieldnames)
writer.writeheader()
writer.writerows(data)
print(f"CSV文件写入成功: {filename}")
except Exception as e:
print(f"写入CSV文件时出错: {e}")
# 使用示例
csv_data = [
["姓名", "年龄", "城市"],
["张三", "25", "北京"],
["李四", "30", "上海"]
]
write_csv_file("people.csv", csv_data)
问题131：如何处理JSON文件？¶
import json
# 1. 读取JSON文件
def read_json_file(filename):
try:
with open(filename, "r", encoding="utf-8") as file:
data = json.load(file)
return data
except FileNotFoundError:
print(f"文件 {filename} 不存在")
return None
except json.JSONDecodeError:
print(f"JSON格式错误")
return None
# 2. 写入JSON文件
def write_json_file(filename, data):
try:
with open(filename, "w", encoding="utf-8") as file:
json.dump(data, file, ensure_ascii=False, indent=2)
print(f"JSON文件写入成功: {filename}")
except Exception as e:
print(f"写入JSON文件时出错: {e}")
# 3. 处理复杂JSON数据
def process_json_data():
# 示例数据
data = {
"users": [
{"name": "张三", "age": 25, "city": "北京"},
{"name": "李四", "age": 30, "city": "上海"}
],
"settings": {
"theme": "dark",
"language": "zh-CN"
}
}
# 写入JSON文件
write_json_file("data.json", data)
# 读取JSON文件
loaded_data = read_json_file("data.json")
if loaded_data:
print("JSON数据加载成功")
print(f"用户数量: {len(loaded_data['users'])}")
问题132：文件操作的最佳实践¶
import os
import shutil
from pathlib import Path
# 1. 安全的文件操作
def safe_file_operation(filename, operation):
try:
# 检查文件是否存在
if not os.path.exists(filename):
print(f"文件 {filename} 不存在")
return False
# 检查文件权限
if not os.access(filename, os.R_OK):
print(f"没有读取权限: {filename}")
return False
# 执行操作
return operation(filename)
except Exception as e:
print(f"操作失败: {e}")
return False
# 2. 文件备份
def backup_file(filename):
if not os.path.exists(filename):
print(f"文件 {filename} 不存在")
return False
backup_name = f"{filename}.backup"
try:
shutil.copy2(filename, backup_name)
print(f"文件备份成功: {backup_name}")
return True
except Exception as e:
print(f"备份失败: {e}")
return False
# 3. 文件清理
def clean_old_files(directory, days=30):
import time
current_time = time.time()
cutoff_time = current_time - (days * 24 * 60 * 60)
try:
for filename in os.listdir(directory):
file_path = os.path.join(directory, filename)
if os.path.isfile(file_path):
file_time = os.path.getmtime(file_path)
if file_time < cutoff_time:
os.remove(file_path)
print(f"删除旧文件: {filename}")
except Exception as e:
print(f"清理文件时出错: {e}")
# 4. 文件监控
def monitor_file_changes(filename):
import time
last_modified = 0
while True:
try:
if os.path.exists(filename):
current_modified = os.path.getmtime(filename)
if current_modified > last_modified:
print(f"文件 {filename} 已修改")
last_modified = current_modified
time.sleep(1)
except KeyboardInterrupt:
print("监控停止")
break
问题133：文件操作的实际应用¶
# 1. 日志文件处理
class Logger:
def __init__(self, filename):
self.filename = filename
def log(self, message, level="INFO"):
import datetime
timestamp = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
log_entry = f"[{timestamp}] {level}: {message}\n"
with open(self.filename, "a", encoding="utf-8") as file:
file.write(log_entry)
def read_logs(self, lines=10):
try:
with open(self.filename, "r", encoding="utf-8") as file:
all_lines = file.readlines()
return all_lines[-lines:]
except FileNotFoundError:
return []
# 2. 配置文件管理
class ConfigManager:
def __init__(self, config_file):
self.config_file = config_file
self.config = {}
self.load_config()
def load_config(self):
try:
with open(self.config_file, "r", encoding="utf-8") as file:
self.config = json.load(file)
except FileNotFoundError:
self.config = {}
except json.JSONDecodeError:
print("配置文件格式错误")
self.config = {}
def save_config(self):
try:
with open(self.config_file, "w", encoding="utf-8") as file:
json.dump(self.config, file, ensure_ascii=False, indent=2)
except Exception as e:
print(f"保存配置失败: {e}")
def get(self, key, default=None):
return self.config.get(key, default)
def set(self, key, value):
self.config[key] = value
self.save_config()
# 3. 文件同步
def sync_files(source_dir, target_dir):
source_path = Path(source_dir)
target_path = Path(target_dir)
if not source_path.exists():
print(f"源目录不存在: {source_dir}")
return
target_path.mkdir(exist_ok=True)
for file_path in source_path.rglob("*"):
if file_path.is_file():
relative_path = file_path.relative_to(source_path)
target_file = target_path / relative_path
target_file.parent.mkdir(parents=True, exist_ok=True)
shutil.copy2(file_path, target_file)
print(f"同步文件: {relative_path}")
总结¶
文件操作是Python编程中的重要技能，要点包括： - 文件打开和关闭：使用with语句确保文件正确关闭 - 文件模式：r、w、a、x等不同模式的使用 - 异常处理：处理文件不存在、权限错误等异常 - 二进制文件：处理图片、视频等二进制数据 - pathlib模块：现代化的路径处理方式 - CSV和JSON：处理结构化数据文件 - 最佳实践：安全操作、备份、监控等 - 实际应用：日志、配置、同步等场景