在 Python 中从 Freebase 中提取数据转储

Question

使用从 website 下载的数据转储 Freebase 三元组 (freebase-rdf-latest.gz)，打开和读取此文件以提取信息的最佳过程是什么，比方说关于公司和企业的相关信息？（在Python）

据我所知，有一些包可以实现这个目标：在 python 中打开 gz 文件并读取 rdf 文件，我不确定如何完成这个...

我在 python 3.6 中的失败尝试：

import gzip

with gzip.open('freebase-rdf-latest.gz','r') as uncompressed_file:
       for line in uncompressed_file.read():
           print(line)

之后使用 xml 结构我可以通过解析它来获取信息，但我无法读取文件。

Answer 1

问题是 gzip 模块一次解压整个文件，将解压后的文件存储在内存中。对于这么大的文件，更实用的方法是一次一点点地解压文件，然后流式传输结果。

#!/usr/bin/env python3
import io
import zlib

def stream_unzipped_bytes(filename):
    """
    Generator function, reads gzip file `filename` and yields
    uncompressed bytes.

    This function answers your original question, how to read the file,
    but its output is a generator of bytes so there's another function
    below to stream these bytes as text, one line at a time.
    """
    with open(filename, 'rb') as f:
        wbits = zlib.MAX_WBITS | 16  # 16 requires gzip header/trailer
        decompressor = zlib.decompressobj(wbits)
        fbytes = f.read(16384)
        while fbytes:
            yield decompressor.decompress(decompressor.unconsumed_tail + fbytes)
            fbytes = f.read(16384)


def stream_text_lines(gen):
    """
    Generator wrapper function, `gen` is a bytes generator.
    Yields one line of text at a time.
    """
    try:
        buf = next(gen)
        while buf:
            lines = buf.splitlines(keepends=True)
            # yield all but the last line, because this may still be incomplete
            # and waiting for more data from gen
            for line in lines[:-1]:
                yield line.decode()
            # set buf to end of prior data, plus next from the generator.
            # do this in two separate calls in case gen is done iterating,
            # so the last output is not lost.
            buf = lines[-1]
            buf += next(gen)
    except StopIteration:
        # yield the final data
        if buf:
            yield buf.decode()


# Sample usage, using the stream_text_lines generator to stream
# one line of RDF text at a time
bytes_generator = (x for x in stream_unzipped_bytes('freebase-rdf-latest.gz'))
for line in stream_text_lines(bytes_generator):
    # do something with `line` of text
    print(line, end='')

在 Python 中从 Freebase 中提取数据转储

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