如何检查 JSON 文件是否不为空并从临时文件夹中的文件正确加载 JSON 数据？

Question

问题是进程从不通过文件中的 "loaded" JSON 数据，我不明白为什么。每次都会创建新文件。

import argparse
import os
import tempfile
import json

storage = argparse.ArgumentParser()
storage.add_argument("--key", help="input key's name")
storage.add_argument("--val", help="value of key", default=None)
args = storage.parse_args()
storage_path = os.path.join(tempfile.gettempdir(), 'storage.data')

with open(storage_path,'r') as f:
    if f.seek(2) is not 2:
        data_base = json.load(f)
        print('loaded that: ',data_base)
    else:
        f.close()
        print('each time I am creating the new one')
        with open(storage_path,'w') as f:
            data_base = {}
        f.close()

if data_base.get(args.key, 'Not found') == 'Not found': 
    if args.val is not None:
        data_base.setdefault(args.key, args.val)
        with open(storage_path, 'w') as f:
            json.dump(data_base, f)
            print('dumped this: ',data_base)

Answer 1

您的代码有很多问题，即

如果文件不存在程序崩溃：

with open(storage_path,'r') as f:

正在打开 storage_path 进行写作，但实际上没有写任何东西：

    print('each time I am creating the new one')
    with open(storage_path,'w') as f:
        data_base = {}
    f.close()

实际上，如果您碰巧有 f.seek(2) == 2，json.load(f) 也会崩溃，因为此时您将文件指针移动到第 3 个字符，因此后续读取 json.load() 会'获取全部内容。

这是一个应该可以工作 AFAICT 的固定版本：

import argparse
import os
import tempfile
import json

storage = argparse.ArgumentParser()
storage.add_argument("--key", help="input key's name")
storage.add_argument("--val", help="value of key", default=None)
args = storage.parse_args()
storage_path = os.path.join(tempfile.gettempdir(), 'storage.data')

data_base = None
if os.path.exists(storage_path):
    with open(storage_path,'r') as f:
        try:
            data_base = json.load(f)
            print('loaded that: ',data_base)
        except Exception as e:
            print("got %s on json.load()" % e)

if data_base is None:
    print('each time I am creating the new one')
    data_base = {}
    with open(storage_path,'w') as f:
        json.dump(data_base, f)

# don't prevent the user to set `"Not found" as value, if might
# be a legitimate value.
# NB : you don't check if `args.key` is actually set... maybe you should ?

sentinel = object()    
if data_base.get(args.key, sentinel) is sentinel:         
    if args.val is not None:
        data_base[args.key] = args.val
        with open(storage_path, 'w') as f:
            json.dump(data_base, f)
            print('dumped this: ',data_base)

如何检查 JSON 文件是否不为空并从临时文件夹中的文件正确加载 JSON 数据？

How to check if JSON file is not empty and load JSON data from file in temp folder correctly?

python

temporary-files