New submission from Marc Garcia:
I'm using the csv module from Python standard library, to read a 1.4Gb file
with 11,157,064 of rows. The file is the Geonames dataset for all countries,
which can be freely downloaded [1].
I'm using this code to read it:
import csv
with open('allCountries.txt', 'r') as fd:
reader = csv.reader(fd, delimiter='\t')
for i, row in enumerate(reader):
pass
print(i + 1) # prints 10381963
print(reader.line_num) # prints 11157064
For some reason, there are around 7% of the rows in the files, that are
skipped. The rows doesn't have anything special (most of them are all ascii
characters, even if the file is in utf-8).
If I create a new file with all the skipped files, and I read it again in the
same way, around 30% of the rows are skipped. So many of them weren't returned
by the iterator when being a part of a bigger file, but now they are.
Note that the attribute line_num has the right number. Also note that if I
remove the delimiter parameter (tab) from the reader, and it uses the default
comma, the iteration on the reader doesn't skip any row.
I checked what I think it's the relevant part of the code [2], but I couldn't
see anything that could cause this bug.
1. http://download.geonames.org/export/dump/allCountries.zip
2. https://hg.python.org/cpython/file/tip/Modules/_csv.c#l787
----------
components: Library (Lib)
messages: 280323
nosy: datapythonista
priority: normal
severity: normal
status: open
title: csv reader loosing rows with big files and tab delimiter
versions: Python 3.5
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Python tracker <[email protected]>
<http://bugs.python.org/issue28642>
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