[Python] FileNotFoundErrorとは？発生原因や対処法・回避方法を解説

try:
    with open('non_existent_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError as e:
    print(f"Error: {e}")

Error: [Errno 2] No such file or directory: 'non_existent_file.txt'

# 誤ったパスを指定
with open('wrong_path/file.txt', 'r') as file:
    content = file.read()

# 存在確認をせずにファイルを開く
with open('user_input_file.txt', 'r') as file:
    content = file.read()

# アクセス権限がないファイルを開こうとする
with open('/root/protected_file.txt', 'r') as file:
    content = file.read()

# ファイルシステムの問題でファイルが見つからない場合
with open('/mnt/disk_error/file.txt', 'r') as file:
    content = file.read()

import os
# 現在の作業ディレクトリを確認
current_directory = os.getcwd()
print(f"Current Directory: {current_directory}")

import os
# パスの正規化
normalized_path = os.path.normpath('folder//subfolder/../file.txt')
print(f"Normalized Path: {normalized_path}")

import os
file_path = 'example.txt'
if os.path.exists(file_path):
    print(f"{file_path} exists.")
else:
    print(f"{file_path} does not exist.")

from pathlib import Path
file_path = Path('example.txt')
if file_path.exists():
    print(f"{file_path} exists.")
else:
    print(f"{file_path} does not exist.")

import os
file_path = 'example.txt'
if os.access(file_path, os.R_OK):
    print(f"{file_path} is readable.")
else:
    print(f"{file_path} is not readable.")

import os
import stat
file_path = 'example.txt'
file_stat = os.stat(file_path)
if file_stat.st_mode & stat.S_IRUSR:
    print(f"{file_path} is readable by the owner.")
else:
    print(f"{file_path} is not readable by the owner.")

try:
    with open('non_existent_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError as e:
    print(f"Error: {e}")

try:
    with open('non_existent_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("指定されたファイルが見つかりません。ファイル名を確認してください。")

import os
file_path = 'example.txt'
if os.path.exists(file_path):
    with open(file_path, 'r') as file:
        content = file.read()
else:
    print(f"{file_path} does not exist. Please check the file path.")

import re
def is_valid_path(path):
    pattern = r'^[\w\-.\\/:]+$'  # 簡単なパスの正規表現
    return re.match(pattern, path) is not None
user_input_path = input("Enter the file path: ")
if is_valid_path(user_input_path):
    print("Valid path.")
else:
    print("Invalid path format.")

import os
directory_path = 'new_folder'
if not os.path.isdir(directory_path):
    os.makedirs(directory_path)
    print(f"Directory {directory_path} created.")
else:
    print(f"Directory {directory_path} already exists.")

import logging
# ログの設定
logging.basicConfig(filename='app.log', level=logging.ERROR)
try:
    with open('non_existent_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError as e:
    logging.error(f"File not found: {e}")
    print("An error occurred. Please check the log file for details.")

import os
input_directory = 'text_files'
output_file = 'combined.txt'
with open(output_file, 'w') as outfile:
    for filename in os.listdir(input_directory):
        if filename.endswith('.txt'):
            file_path = os.path.join(input_directory, filename)
            if os.path.exists(file_path):
                with open(file_path, 'r') as infile:
                    outfile.write(infile.read() + '\n')
            else:
                print(f"{file_path} does not exist.")

import pandas as pd
import os
file_path = 'data.csv'
if os.path.exists(file_path):
    data = pd.read_csv(file_path)
    data.fillna(0, inplace=True)  # 欠損値を0で埋める
    print(data.head())
else:
    print(f"{file_path} does not exist. Please check the file path.")

import os
import time
log_directory = 'logs'
expiration_days = 30
current_time = time.time()
for filename in os.listdir(log_directory):
    file_path = os.path.join(log_directory, filename)
    if os.path.isfile(file_path):
        file_age = current_time - os.path.getmtime(file_path)
        if file_age > expiration_days * 86400:  # 日数を秒に変換
            os.remove(file_path)
            print(f"Deleted old log file: {file_path}")

import os
import logging
# ログの設定
logging.basicConfig(filename='batch_processing.log', level=logging.ERROR)
input_files = ['file1.txt', 'file2.txt', 'file3.txt']
for file_name in input_files:
    try:
        with open(file_name, 'r') as file:
            content = file.read()
            # ここで何らかの処理を行う
    except FileNotFoundError as e:
        logging.error(f"File not found: {file_name} - {e}")
        print(f"Error processing {file_name}. Check the log for details.")