python - 在 python 中读取 bz2 文件的第一行

Question

我正在尝试从 bz2 文件中提取 10'000 行。

   import bz2       
   file = "file.bz2"
   file_10000 = "file.txt"

   output_file = codecs.open(file_10000,'w+','utf-8')

   source_file = bz2.open(file, "r")
   count = 0
   for line in source_file:
       count += 1
       if count < 10000:
           output_file.writerow(line)

但我得到一个错误“‘模块’对象没有属性‘打开’”。你有什么想法？或者我可以通过其他方式将 10'000 行保存到 txt 文件中吗？我在 Windows 上。

Answer 1

这是一个完整的示例，其中包括编写和读取一个比您的 10000 行小得多的测试文件。很高兴在问题中有工作示例，这样我们就可以轻松测试。

import bz2
import itertools
import codecs

file = "file.bz2"
file_10000 = "file.txt"

# write test file with 9 lines
with bz2.BZ2File(file, "w") as fp:
    fp.write('\n'.join('123456789'))

# the original script using BZ2File ... and 3 lines for test
# ...and fixing bugs:
#     1) it only writes 9999 instead of 10000
#     2) files don't do writerow
#     3) close the files

output_file = codecs.open(file_10000,'w+','utf-8')

source_file = bz2.BZ2File(file, "r")
count = 0
for line in source_file:
    count += 1
    if count <= 3:
       output_file.write(line)
source_file.close()
output_file.close()

# show what you got
print('---- Test 1 ----')
print(repr(open(file_10000).read()))   

一种更有效的方法是在阅读所需行后跳出 for 循环。您甚至可以像这样利用迭代器来精简代码:

# a faster way to read first 3 lines
with bz2.BZ2File(file) as source_file,\
        codecs.open(file_10000,'w+','utf-8') as output_file:
    output_file.writelines(itertools.islice(source_file, 3))

# show what you got
print('---- Test 2 ----')
print(repr(open(file_10000).read()))