python - 在 Python 中读取大型 JSON 文件 (raw_decode)

Question

我正在尝试在 Python 中读取大型 JSON 文件 (data.json)。因为JSON文件有多个JSON对象，Python会创建多个字典(字典数量未知)，所以我使用了decoder.raw_decode()和generator。 以下是代码:

import json
import pprint
import io
import pprint

def parse():

    with open('data.json',encoding='utf-8') as jfile:
        try:
            while True:
                decoder = json.JSONDecoder()
                obj, idx = decoder.raw_decode(jfile)
                yield obj
        except ValueError as e:
            print(e)
            pass
        else:
            print("aha")


def main():
    imputd=parse()
    if imputd: 
        while True:
            try:
                print(str(next(imputd)).readlines())
            except StopIteration as e:
                print(e)
                break

main()

我得到错误:

Traceback (most recent call last):
  File "H:\Document\Python\j10.py", line 57, in <module>
    main()
  File "H:\Document\Python\j10.py", line 36, in main
    print(str(next(imputd)).readlines())
  File "H:\Document\Python\j10.py", line 21, in parse
    obj, idx = decoder.raw_decode(jfile)
  File "C:\Python34\lib\json\decoder.py", line 360, in raw_decode
    obj, end = self.scan_once(s, idx)
TypeError: first argument must be a string, not _io.TextIOWrapper

我根据 Martijn 的回答编辑了代码:

import json
import io



file=open('data.json.txt')
def readin():
    return file.read(2000)


def parse():
    decoder = json.JSONDecoder()
    buffer = ''    
    for chunk in iter(readin, ''):
        buffer += chunk
        while buffer:
            try:
                result, index = decoder.raw_decode(buffer)
                yield result
                buffer = buffer[index:]
            except ValueError:
                 # Not enough data to decode, read more
                break

def main():
    imputd=parse()
    if imputd: 
        while True:
            try:
                print(str(next(imputd)).readlines())
            except StopIteration as e:
                print(e)
                break

main()

我得到一个 UnicodeError:

Traceback (most recent call last):
  File "H:\Document\Python\j11.py", line 35, in <module>
    main()
  File "H:\Document\Python\j11.py", line 30, in main
    print(str(next(imputd)).readlines())
  File "H:\Document\Python\j11.py", line 14, in parse
    for chunk in iter(readin, ''):
  File "H:\Document\Python\j11.py", line 8, in readin
    return file.read(2000)
  File "C:\Python34\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 4217: character maps to <undefined>

Answer 1

您正在传递文件对象，但 decoder.raw_decode() 只接受文本数据。您需要自己阅读:

obj, idx = decoder.raw_decode(jfile.read())

然后您将生成 从 JSON 数据创建的 Python 对象，因此您在 main() 函数循环中调用 .readlines()也会失败。

但是，您没有正确使用 raw_decode()。您自己负责向它提供文本 block ，它不会为您从文件中读取该文本。如果您想分块处理文件，并且 JSON 条目之间没有明确的分隔符，您将被迫分块读取文件:

decoder = json.JSONDecoder()
buffer = ''
for chunk in iter(partial(jfile.read, buffersize), ''):
     buffer += chunk
     while buffer:
         try:
             result, index = decoder.raw_decode(buffer)
             yield result
             buffer = buffer[index:]
         except ValueError:
             # Not enough data to decode, read more
             break

这仍然会产生完全解码的对象；如果您的文件是一个长 JSON 对象(例如一个顶级列表或字典)，那么这将不会逐一生成该对象的内容；它仍然会在屈服之前读取整个对象。