如何在Python中读取大文件的特定部分
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How to read specific part of large file in Python
提问by Cerin
Given a large file (hundreds of MB) how would I use Python to quickly read the content between a specific start and end index within the file?
给定一个大文件（数百 MB），我将如何使用 Python 快速读取文件中特定开始和结束索引之间的内容？
Essentially, I'm looking for a more efficient way of doing:
本质上，我正在寻找一种更有效的方法：
open(filename).read()[start_index:end_index]
采纳答案by Dan Lecocq
You can seekinto the file the file and then read a certain amount from there. Seek allows you to get to a specific offset within a file, and then you can limit your read to only the number of bytes in that range.
您可以seek将文件放入文件中，然后从那里读取一定数量的文件。Seek 允许您获得文件内的特定偏移量，然后您可以将读取限制为该范围内的字节数。
with open(filename) as fin:
fin.seek(start_index)
data = fin.read(end_index - start_index)
That will only read that data that you're looking for.
那只会读取您正在寻找的数据。
回答by Will Leeney
This is my solution with variable width encoding. My CSV file contains a dictionary where each row is a new item.
这是我的可变宽度编码解决方案。我的 CSV 文件包含一个字典，其中每一行都是一个新项目。
def get_stuff(filename, count, start_index):
with open(filename, 'r') as infile:
reader = csv.reader(infile)
num = 0
for idx, row in enumerate(reader):
if idx >= start_index-1:
if num >= count:
return
else:
yield row
num += 1
