[Solved] Python CSV error: line contains NULL byte

I’m working with some CSV files, with the following code:

reader = csv.reader(open(filepath, "rU"))
    for row in reader:
        print 'Row read successfully!', row
except csv.Error, e:
    sys.exit('file %s, line %d: %s' % (filename, reader.line_num, e))

And one file is throwing this error:

file my.csv, line 1: line contains NULL byte

What can I do? Google seems to suggest that it may be an Excel file that’s been saved as a .csv improperly. Is there any way I can get round this problem in Python?

== UPDATE ==

Following @JohnMachin’s comment below, I tried adding these lines to my script:

print repr(open(filepath, 'rb').read(200)) # dump 1st 200 bytes of file
data = open(filepath, 'rb').read()
print data.find('x00')
print data.count('x00')

And this is the output I got:

'xd0xcfx11xe0xa1xb1x1axe1x00x00x00x00x00x00x00x00 .... <snip>

So the file does indeed contain NUL bytes.

Enquirer: AP257


Solution #1:

As @S.Lott says, you should be opening your files in ‘rb’ mode, not ‘rU’ mode. However that may NOT be causing your current problem. As far as I know, using ‘rU’ mode would mess you up if there are embedded r in the data, but not cause any other dramas. I also note that you have several files (all opened with ‘rU’ ??) but only one causing a problem.

If the csv module says that you have a “NULL” (silly message, should be “NUL”) byte in your file, then you need to check out what is in your file. I would suggest that you do this even if using ‘rb’ makes the problem go away.

repr() is (or wants to be) your debugging friend. It will show unambiguously what you’ve got, in a platform independant fashion (which is helpful to helpers who are unaware what od is or does). Do this:

print repr(open('my.csv', 'rb').read(200)) # dump 1st 200 bytes of file

and carefully copy/paste (don’t retype) the result into an edit of your question (not into a comment).

Also note that if the file is really dodgy e.g. no r or n within reasonable distance from the start of the file, the line number reported by reader.line_num will be (unhelpfully) 1. Find where the first x00 is (if any) by doing

data = open('my.csv', 'rb').read()
print data.find('x00')

and make sure that you dump at least that many bytes with repr or od.

What does data.count('x00') tell you? If there are many, you may want to do something like

for i, c in enumerate(data):
    if c == 'x00':
        print i, repr(data[i-30:i]) + ' *NUL* ' + repr(data[i+1:i+31])

so that you can see the NUL bytes in context.

If you can see x00 in the output (or in your od -c output), then you definitely have NUL byte(s) in the file, and you will need to do something like this:

fi = open('my.csv', 'rb')
data =
fo = open('mynew.csv', 'wb')
fo.write(data.replace('x00', ''))

By the way, have you looked at the file (including the last few lines) with a text editor? Does it actually look like a reasonable CSV file like the other (no “NULL byte” exception) files?

Respondent: AP257

Solution #2:

data_initial = open("staff.csv", "rb")
data = csv.reader((line.replace('','') for line in data_initial), delimiter=",")

This works for me.

Respondent: John Machin

Solution #3:

Reading it as UTF-16 was also my problem.

Here’s my code that ended up working:,"rb","utf-16")
for row in csvread:
    print row

Where location is the directory of your csv file.

Respondent: double

Solution #4:

I bumped into this problem as well. Using the Python csv module, I was trying to read an XLS file created in MS Excel and running into the NULL byte error you were getting. I looked around and found the xlrd Python module for reading and formatting data from MS Excel spreadsheet files. With the xlrd module, I am not only able to read the file properly, but I can also access many different parts of the file in a way I couldn’t before.

I thought it might help you.

Respondent: User

Solution #5:

Converting the encoding of the source file from UTF-16 to UTF-8 solve my problem.

How to convert a file to utf-8 in Python?

import codecs
BLOCKSIZE = 1048576 # or some other, desired size in bytes
with, "r", "utf-16") as sourceFile:
    with, "w", "utf-8") as targetFile:
        while True:
            contents =
            if not contents:
Respondent: ayaz

Solution #6:

You could just inline a generator to filter out the null values if you want to pretend they don’t exist. Of course this is assuming the null bytes are not really part of the encoding and really are some kind of erroneous artifact or bug.

with open(filepath, "rb") as f:
    reader = csv.reader( (line.replace('','') for line in f) )

        for row in reader:
            print 'Row read successfully!', row
    except csv.Error, e:
        sys.exit('file %s, line %d: %s' % (filename, reader.line_num, e))
Respondent: Patrick Halley

Solution #7:

Why are you doing this?

 reader = csv.reader(open(filepath, "rU"))

The docs are pretty clear that you must do this:

with open(filepath, "rb") as src:
    reader= csv.reader( src )

The mode must be “rb” to read.

If csvfile is a file object, it must be opened with the ‘b’ flag on platforms where that makes a difference.

Respondent: woot

Solution #8:

appparently it’s a XLS file and not a CSV file as confirm

Respondent: S.Lott

Solution #9:

Instead of csv reader I use read file and split function for string:

lines = open(input_file,'rb') 

for line_all in lines:

    line=line_all.replace('x00', '').split(";")
Respondent: Xavier Combelle

Solution #10:

I got the same error. Saved the file in UTF-8 and it worked.

Respondent: Nico The Brush

Solution #11:

This happened to me when I created a CSV file with OpenOffice Calc. It didn’t happen when I created the CSV file in my text editor, even if I later edited it with Calc.

I solved my problem by copy-pasting in my text editor the data from my Calc-created file to a new editor-created file.

Respondent: mikaiscute

Solution #12:

I had the same problem opening a CSV produced from a webservice which inserted NULL bytes in empty headers. I did the following to clean the file:

with ('my.csv', 'rb', 'utf-8') as myfile:
    data =
    # clean file first if dirty
    if data.count( 'x00' ):
        print 'Cleaning...'
        with'my.csv.tmp', 'w', 'utf-8') as of:
            for line in data:
                of.write(line.replace('x00', ''))

        shutil.move( 'my.csv.tmp', 'my.csv' )

with ('my.csv', 'rb', 'utf-8') as myfile:
    myreader = csv.reader(myfile, delimiter=',')
    # Continue with your business logic here...

Be aware that this overwrites your original data. Make sure you have a backup copy of it. You have been warned!

Respondent: user1990371

Solution #13:

For all those ‘rU’ filemode haters: I just tried opening a CSV file from a Windows machine on a Mac with the ‘rb’ filemode and I got this error from the csv module:

Error: new-line character seen in unquoted field - do you need to 
open the file in universal-newline mode?

Opening the file in ‘rU’ mode works fine. I love universal-newline mode — it saves me so much hassle.

Respondent: Matthias Kuhn

Solution #14:

I encountered this when using scrapy and fetching a zipped csvfile without having a correct middleware to unzip the response body before handing it to the csvreader. Hence the file was not really a csv file and threw the line contains NULL byte error accordingly.

Respondent: Bill Gross

Solution #15:

Have you tried using

with'my.csv', 'rb') as data_file:

I was trying to open a file that had been compressed but had the extension ‘.csv’ instead of ‘csv.gz’. This error kept showing up until I used

Respondent: Gesias

Solution #16:

One case is that – If the CSV file contains empty rows this error may show up. Check for row is necessary before we proceed to write or read.

for row in csvreader:
        if (row):       
            do something

I solved my issue by adding this check in the code.

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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