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Stream Bytes chunks to csv rows in python

I need to process a large remote CSV line by line without downloading it entirely.
Below is the closest I got.
I iterate byte chunks from Azure, and have some code to handle truncated lines.
But this cannot work if csv values contain a newline as I am not able to discernate between value newlines and csv newlines.
# this does not work
def azure_iter_lines(logger_scope, client, file_path):
# get a StorageStreamDownloader
# https://learn.microsoft.com/en-us/python/api/azure-storage-file-datalake/azure.storage.filedatalake.storagestreamdownloader?view=azure-python
file_client = client.get_file_client(file_path)
file_handle = file_client.download_file()
truncated_line = ''
for chunk in file_handle.chunks():
# have the previous truncated line appended to the next block
chunk_txt = truncated_line + chunk.decode("utf-8")
lines = chunk_txt.split('\n') # THIS CANNOT WORK AS VALUES CONTAIN NEWLINES
for line in lines[0:len(lines)-2]:
yield line
truncated_line = lines[len(lines)-1]
# process the last chunk (same code)
chunk_txt = truncated_line
lines = chunk_txt.split('\n') # THIS CANNOT WORK AS VALUES CONTAIN NEWLINES
for line in lines[0:len(lines)-2]:
yield line
truncated_line = lines[len(lines)-1]
Ideally I would use csv.DictReader() but I was not able to to so as it downloads the file entirely.
# this does not work
def azure_iter_lines(logger_scope, client, file_path):
file_client = client.get_file_client(file_path)
file_handle = file_client.download_file()
buffer = io.BytesIO()
file_handle.readinto(buffer) # THIS DOWNLOADS THE FILE ENTIRELY
csvreader = csv.DictReader(buffer, delimiter=";")
return csvreader
Here is an update using some hints by #H.Leger
Please note that this still does not work
file_client = client.get_file_client(file_path)
file_handle = file_client.download_file()
stream = codecs.iterdecode(file_handle.chunks(), 'utf-8')
csvreader = csv.DictReader(stream, delimiter=";")
for row in csvreader:
print(row)
# => _csv.Error: new-line character seen in unquoted field - do you need to open the file in universal-newline mode?
EDIT: Final solution based on #paiv answer
EDIT: Updated solution to use io instead of codecs for faster parsing
import io
import csv
import ctypes as ct
# bytes chunk iterator to python stream adapter
# https://stackoverflow.com/a/67547597/2523414
class ChunksAdapter:
def __init__(self, chunks):
self.chunks = chunks
self.buf = b''
self.closed = False
def readable(self):
return True
def writable(self):
return False
def seekable(self):
return False
def close(self):
self.closed = True
def read(self, size):
if not self.buf:
self.buf = next(self.chunks, b'')
res, self.buf = self.buf[:size], self.buf[size:]
return res
# get the downloader object
file_client = client.get_file_client(file_path)
downloader = file_client.download_file()
# adapt the downloader iterator to a byte stream
file_object = ChunksAdapter(downloader.chunks())
# decode bytes stream to utf-8
text_stream = io.TextIOWrapper(file_object, encoding='utf-8', newline='')
# update csv field limit to handle large fields
# https://stackoverflow.com/a/54517228/2523414
csv.field_size_limit(int(ct.c_ulong(-1).value // 2))
csvreader = csv.DictReader(text_stream, delimiter=";", quotechar='"', quoting=csv.QUOTE_MINIMAL)
for row in csvreader:
print(row)

Disclaimer: I know little Azure specifics. Ultimately, you would want to stream separate chunks too.
In Python, given a file object, you can set up CSV streaming this way:
import codecs
import csv
codec = codecs.getreader('utf-8')
text_stream = codec(file_object)
csvreader = csv.DictReader(text_stream)
Now you can iterate over csvreader, and it will read from file_object in a streaming fasion.
Edit: as #Martijn Pieters suggested, we can gain performance with TextIOWrapper instead of codecs:
text_stream = io.TextIOWrapper(file_object, encoding='utf-8', newline='')
Check the comment in csv module on newline parameter.
But Azure's StorageStreamDownloader does not provide python's file object interface. It has .chunks() generator (which I assume will invoke separate HTTP request to retrieve next chunk).
You can adapt .chunks() into a file object with a simple adapter:
class ChunksAdapter:
def __init__(self, chunks):
self.chunks = chunks
self.buf = b''
def read(self, size):
if not self.buf:
self.buf = next(self.chunks, b'')
res, self.buf = self.buf[:size], self.buf[size:]
return res
And use like
downloader = file_client.download_file()
file_object = ChunksAdapter(downloader.chunks())
Be sure to configure DictReader for the appropriate CSV dialect.
And set appropriate values for max_single_get_size, max_chunk_get_size on the blob client.

I believe the requests package can be useful for you. Using the stream option while getting your file and the Response.iter_lines() function should do what you need :
import codecs
import csv
import requests
url = "https://navitia.opendatasoft.com//explore/dataset/all-datasets/download?format=csv"
r = requests.get(url, stream=True) # using the stream option to avoid loading everything
try:
buffer = r.iter_lines() # iter_lines() will feed you the distant file line by line
reader = csv.DictReader(codecs.iterdecode(buffer, 'utf-8'), delimiter=';')
for row in reader:
print(row) # Do stuff here
finally:
r.close()

How to use "encoding" argument in Python 2 for the open() function? [duplicate]

I am new to Python, and I have a question about how to use Python to read and write CSV files. My file contains like Germany, French, etc. According to my code, the files can be read correctly in Python, but when I write it into a new CSV file, the unicode becomes some strange characters.
The data is like:
And my code is:
import csv
f=open('xxx.csv','rb')
reader=csv.reader(f)
wt=open('lll.csv','wb')
writer=csv.writer(wt,quoting=csv.QUOTE_ALL)
wt.close()
f.close()
And the result is like:
What should I do to solve the problem?

Another alternative:
Use the code from the unicodecsv package ...
https://pypi.python.org/pypi/unicodecsv/
>>> import unicodecsv as csv
>>> from io import BytesIO
>>> f = BytesIO()
>>> w = csv.writer(f, encoding='utf-8')
>>> _ = w.writerow((u'é', u'ñ'))
>>> _ = f.seek(0)
>>> r = csv.reader(f, encoding='utf-8')
>>> next(r) == [u'é', u'ñ']
True
This module is API compatible with the STDLIB csv module.

Make sure you encode and decode as appropriate.
This example will roundtrip some example text in utf-8 to a csv file and back out to demonstrate:
# -*- coding: utf-8 -*-
import csv
tests={'German': [u'Straße',u'auslösen',u'zerstören'],
'French': [u'français',u'américaine',u'épais'],
'Chinese': [u'中國的',u'英語',u'美國人']}
with open('/tmp/utf.csv','w') as fout:
writer=csv.writer(fout)
writer.writerows([tests.keys()])
for row in zip(*tests.values()):
row=[s.encode('utf-8') for s in row]
writer.writerows([row])
with open('/tmp/utf.csv','r') as fin:
reader=csv.reader(fin)
for row in reader:
temp=list(row)
fmt=u'{:<15}'*len(temp)
print fmt.format(*[s.decode('utf-8') for s in temp])
Prints:
German Chinese French
Straße 中國的 français
auslösen 英語 américaine
zerstören 美國人 épais

There is an example at the end of the csv module documentation that demonstrates how to deal with Unicode. Below is copied directly from that example. Note that the strings read or written will be Unicode strings. Don't pass a byte string to UnicodeWriter.writerows, for example.
import csv,codecs,cStringIO
class UTF8Recoder:
def __init__(self, f, encoding):
self.reader = codecs.getreader(encoding)(f)
def __iter__(self):
return self
def next(self):
return self.reader.next().encode("utf-8")
class UnicodeReader:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
f = UTF8Recoder(f, encoding)
self.reader = csv.reader(f, dialect=dialect, **kwds)
def next(self):
'''next() -> unicode
This function reads and returns the next line as a Unicode string.
'''
row = self.reader.next()
return [unicode(s, "utf-8") for s in row]
def __iter__(self):
return self
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
'''writerow(unicode) -> None
This function takes a Unicode string and encodes it to the output.
'''
self.writer.writerow([s.encode("utf-8") for s in row])
data = self.queue.getvalue()
data = data.decode("utf-8")
data = self.encoder.encode(data)
self.stream.write(data)
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
with open('xxx.csv','rb') as fin, open('lll.csv','wb') as fout:
reader = UnicodeReader(fin)
writer = UnicodeWriter(fout,quoting=csv.QUOTE_ALL)
for line in reader:
writer.writerow(line)
Input (UTF-8 encoded):
American,美国人
French,法国人
German,德国人
Output:
"American","美国人"
"French","法国人"
"German","德国人"

Because str in python2 is bytes actually. So if want to write unicode to csv, you must encode unicode to str using utf-8 encoding.
def py2_unicode_to_str(u):
# unicode is only exist in python2
assert isinstance(u, unicode)
return u.encode('utf-8')
Use class csv.DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds):
py2
The csvfile: open(fp, 'w')
pass key and value in bytes which are encoded with utf-8
writer.writerow({py2_unicode_to_str(k): py2_unicode_to_str(v) for k,v in row.items()})
py3
The csvfile: open(fp, 'w')
pass normal dict contains str as row to writer.writerow(row)
Finally code
import sys
is_py2 = sys.version_info[0] == 2
def py2_unicode_to_str(u):
# unicode is only exist in python2
assert isinstance(u, unicode)
return u.encode('utf-8')
with open('file.csv', 'w') as f:
if is_py2:
data = {u'Python中国': u'Python中国', u'Python中国2': u'Python中国2'}
# just one more line to handle this
data = {py2_unicode_to_str(k): py2_unicode_to_str(v) for k, v in data.items()}
fields = list(data[0])
writer = csv.DictWriter(f, fieldnames=fields)
for row in data:
writer.writerow(row)
else:
data = {'Python中国': 'Python中国', 'Python中国2': 'Python中国2'}
fields = list(data[0])
writer = csv.DictWriter(f, fieldnames=fields)
for row in data:
writer.writerow(row)
Conclusion
In python3, just use the unicode str.
In python2, use unicode handle text, use str when I/O occurs.

I had the very same issue. The answer is that you are doing it right already. It is the problem of MS Excel. Try opening the file with another editor and you will notice that your encoding was successful already. To make MS Excel happy, move from UTF-8 to UTF-16. This should work:
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel_tab, encoding="utf-16", **kwds):
# Redirect output to a queue
self.queue = StringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
# Force BOM
if encoding=="utf-16":
import codecs
f.write(codecs.BOM_UTF16)
self.encoding = encoding
def writerow(self, row):
# Modified from original: now using unicode(s) to deal with e.g. ints
self.writer.writerow([unicode(s).encode("utf-8") for s in row])
# Fetch UTF-8 output from the queue ...
data = self.queue.getvalue()
data = data.decode("utf-8")
# ... and reencode it into the target encoding
data = data.encode(self.encoding)
# strip BOM
if self.encoding == "utf-16":
data = data[2:]
# write to the target stream
self.stream.write(data)
# empty queue
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)

I couldn't respond to Mark above, but I just made one modification which fixed the error that was caused if data in the cells was not unicode, e.g. float or int data. I replaced this line into the UnicodeWriter function: "self.writer.writerow([s.encode("utf-8") if type(s)==types.UnicodeType else s for s in row])" so that it became:
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
'''writerow(unicode) -> None
This function takes a Unicode string and encodes it to the output.
'''
self.writer.writerow([s.encode("utf-8") if type(s)==types.UnicodeType else s for s in row])
data = self.queue.getvalue()
data = data.decode("utf-8")
data = self.encoder.encode(data)
self.stream.write(data)
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
You will also need to "import types".

I don't think this is the best answer, but it's probably the most self-contained answer and also the funniest.
UTF7 is a 7-bit ASCII encoding of unicode. It just so happens that UTF7 makes no special use of commas, quotes, or whitespace. It just passes them through from input to output. So really it makes no difference if you UTF7-encode first and then parse as CSV, or if you parse as CSV first and then UTF7-encode. Python 2's CSV parser can't handle unicode, but python 2 does have a UTF-7 encoder. So you can encode, parse, and then decode, and it's as if you had a unicode-capable parser.
import csv
import io
def read_csv(path):
with io.open(path, 'rt', encoding='utf8') as f:
lines = f.read().split("\r\n")
lines = [l.encode('utf7').decode('ascii') for l in lines]
reader = csv.reader(lines, dialect=csv.excel)
for row in reader:
yield [x.encode('ascii').decode('utf7') for x in row]
for row in read_csv("lol.csv"):
print(repr(row))
lol.csv
foo,bar,foo∆bar,"foo,bar"
output:
[u'foo', u'bar', u'foo\u2206bar', u'foo,bar']

Trouble on Unicode encoded data in Python

Hello StackOverflow community.
I am a fairly new user of Python, so sorry in advance for the sillyness of this question ! But I have tried to fix it out for hours but still not having figured it out.
I am trying to import a large dataset of text to manipulate it in Python.
This data set is in .csv and I've had problems reading it because of encoding problems.
I have tried to encode it in UTF-8 text with notepad++
I have tried the csv.reader module in Python
Here is an example of my code :
import csv
with open('twitter_test_python.csv') as csvfile:
#for file5 in csvfile:
# file5.readline()
#csvfile = csvfile.encode('utf-8')
spamreader = csv.reader(csvfile, delimiter=str(','), quotechar=str('|')
for row in spamreader:
row = " ".join(row)
row2= str.split(row)
listsw = []
for mots in row2:
if mots not in sw:
del mots
print row2
But when I import my data in Python I still have encoding problems (accents, etc) whether method I use.
How can I encode my data so that it is readable properly with Python ?
Thanks !

csv module documentation provides an example of how to deal with unicode:
import csv,codecs,cStringIO
class UTF8Recoder:
def __init__(self, f, encoding):
self.reader = codecs.getreader(encoding)(f)
def __iter__(self):
return self
def next(self):
return self.reader.next().encode("utf-8")
class UnicodeReader:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
f = UTF8Recoder(f, encoding)
self.reader = csv.reader(f, dialect=dialect, **kwds)
def next(self):
'''next() -> unicode
This function reads and returns the next line as a Unicode string.
'''
row = self.reader.next()
return [unicode(s, "utf-8") for s in row]
def __iter__(self):
return self
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
'''writerow(unicode) -> None
This function takes a Unicode string and encodes it to the output.
'''
self.writer.writerow([s.encode("utf-8") for s in row])
data = self.queue.getvalue()
data = data.decode("utf-8")
data = self.encoder.encode(data)
self.stream.write(data)
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
with open('twitter_test_python.csv','rb') as spamreader:
reader = UnicodeReader(fin)
for line in reader:
#do stuff
print line

Alexey Smirnov's answer is elegant but maybe a bit complicated for a beginner. So let me give an example closer to the code in the question.
When you read in files with Python 2 you get the content as str, not unicode. Probably you want to convert it as soon as possible. However, the documentation of the csv module says "This version of the csv module doesn’t support Unicode input." So you should encode the output of csv.reader, not the input. Inserting it into your code results in:
import csv
with open('twitter_test_python.csv') as csvfile:
spamreader = csv.reader(csvfile, delimiter=str(','), quotechar=str('|'))
for row in spamreader:
row = " ".join(row)
row = unicode(row, encoding="utf-8")
row2 = row.split()
However, you might want to consider whether joining the cells just to split them again is really what you want. Without that the code would look like following. The result is different if the list elements contain spaces.
import csv
with open('twitter_test_python.csv') as csvfile:
spamreader = csv.reader(csvfile, delimiter=str(','), quotechar=str('|'))
for row in spamreader:
row2 = list(unicode(cell, encoding="utf-8") for cell in row)
If you want to write something back to a file you should convert the unicode first back to a str like unicode.encode("utf-8").

UnicodeDecodeError: while writing into a file

I get this error while writing into a file. How can I handle this.
Traceback (most recent call last):
File "C:\Python27\AureusBAXProjectFB.py", line 278, in <module>
rows = [[unicode(x) for x in row] for row in outlist]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe0 in position 0: ordinal not in range(128)
>>>
Code for writing into a file
class UnicodeWriter:
"""
A CSV writer which will write rows to CSV file "f",
which is encoded in the given encoding.
"""
def __init__(self, f, dialect=csv.excel, encoding="utf-8", **kwds):
# Redirect output to a queue
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
self.writer.writerow([s.encode("utf-8") for s in row])
# Fetch UTF-8 output from the queue ...
data = self.queue.getvalue()
data = data.decode("utf-8")
# ... and reencode it into the target encoding
data = self.encoder.encode(data)
# write to the target stream
self.stream.write(data)
# empty queue
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
with open('C:/Users/Desktop/fboutput.csv', 'wb') as f:
writer = UnicodeWriter(f)
rows = [[unicode(x) for x in row] for row in outlist]
writer.writerows(rows)
I am using BeautifulSoup to parse the html data and thats working fine. I get an error only while writing into a file.

unicode() constructor defined as unicode(string[, encoding, errors]) and encoding has default is ascii. If multi-byte string is in outlist, you should appoint unicode encode like utf-8.

Read and Write CSV files including unicode with Python 2.7

I am new to Python, and I have a question about how to use Python to read and write CSV files. My file contains like Germany, French, etc. According to my code, the files can be read correctly in Python, but when I write it into a new CSV file, the unicode becomes some strange characters.
The data is like:
And my code is:
import csv
f=open('xxx.csv','rb')
reader=csv.reader(f)
wt=open('lll.csv','wb')
writer=csv.writer(wt,quoting=csv.QUOTE_ALL)
wt.close()
f.close()
And the result is like:
What should I do to solve the problem?

Another alternative:
Use the code from the unicodecsv package ...
https://pypi.python.org/pypi/unicodecsv/
>>> import unicodecsv as csv
>>> from io import BytesIO
>>> f = BytesIO()
>>> w = csv.writer(f, encoding='utf-8')
>>> _ = w.writerow((u'é', u'ñ'))
>>> _ = f.seek(0)
>>> r = csv.reader(f, encoding='utf-8')
>>> next(r) == [u'é', u'ñ']
True
This module is API compatible with the STDLIB csv module.

Make sure you encode and decode as appropriate.
This example will roundtrip some example text in utf-8 to a csv file and back out to demonstrate:
# -*- coding: utf-8 -*-
import csv
tests={'German': [u'Straße',u'auslösen',u'zerstören'],
'French': [u'français',u'américaine',u'épais'],
'Chinese': [u'中國的',u'英語',u'美國人']}
with open('/tmp/utf.csv','w') as fout:
writer=csv.writer(fout)
writer.writerows([tests.keys()])
for row in zip(*tests.values()):
row=[s.encode('utf-8') for s in row]
writer.writerows([row])
with open('/tmp/utf.csv','r') as fin:
reader=csv.reader(fin)
for row in reader:
temp=list(row)
fmt=u'{:<15}'*len(temp)
print fmt.format(*[s.decode('utf-8') for s in temp])
Prints:
German Chinese French
Straße 中國的 français
auslösen 英語 américaine
zerstören 美國人 épais

There is an example at the end of the csv module documentation that demonstrates how to deal with Unicode. Below is copied directly from that example. Note that the strings read or written will be Unicode strings. Don't pass a byte string to UnicodeWriter.writerows, for example.
import csv,codecs,cStringIO
class UTF8Recoder:
def __init__(self, f, encoding):
self.reader = codecs.getreader(encoding)(f)
def __iter__(self):
return self
def next(self):
return self.reader.next().encode("utf-8")
class UnicodeReader:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
f = UTF8Recoder(f, encoding)
self.reader = csv.reader(f, dialect=dialect, **kwds)
def next(self):
'''next() -> unicode
This function reads and returns the next line as a Unicode string.
'''
row = self.reader.next()
return [unicode(s, "utf-8") for s in row]
def __iter__(self):
return self
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
'''writerow(unicode) -> None
This function takes a Unicode string and encodes it to the output.
'''
self.writer.writerow([s.encode("utf-8") for s in row])
data = self.queue.getvalue()
data = data.decode("utf-8")
data = self.encoder.encode(data)
self.stream.write(data)
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
with open('xxx.csv','rb') as fin, open('lll.csv','wb') as fout:
reader = UnicodeReader(fin)
writer = UnicodeWriter(fout,quoting=csv.QUOTE_ALL)
for line in reader:
writer.writerow(line)
Input (UTF-8 encoded):
American,美国人
French,法国人
German,德国人
Output:
"American","美国人"
"French","法国人"
"German","德国人"

Because str in python2 is bytes actually. So if want to write unicode to csv, you must encode unicode to str using utf-8 encoding.
def py2_unicode_to_str(u):
# unicode is only exist in python2
assert isinstance(u, unicode)
return u.encode('utf-8')
Use class csv.DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds):
py2
The csvfile: open(fp, 'w')
pass key and value in bytes which are encoded with utf-8
writer.writerow({py2_unicode_to_str(k): py2_unicode_to_str(v) for k,v in row.items()})
py3
The csvfile: open(fp, 'w')
pass normal dict contains str as row to writer.writerow(row)
Finally code
import sys
is_py2 = sys.version_info[0] == 2
def py2_unicode_to_str(u):
# unicode is only exist in python2
assert isinstance(u, unicode)
return u.encode('utf-8')
with open('file.csv', 'w') as f:
if is_py2:
data = {u'Python中国': u'Python中国', u'Python中国2': u'Python中国2'}
# just one more line to handle this
data = {py2_unicode_to_str(k): py2_unicode_to_str(v) for k, v in data.items()}
fields = list(data[0])
writer = csv.DictWriter(f, fieldnames=fields)
for row in data:
writer.writerow(row)
else:
data = {'Python中国': 'Python中国', 'Python中国2': 'Python中国2'}
fields = list(data[0])
writer = csv.DictWriter(f, fieldnames=fields)
for row in data:
writer.writerow(row)
Conclusion
In python3, just use the unicode str.
In python2, use unicode handle text, use str when I/O occurs.

I had the very same issue. The answer is that you are doing it right already. It is the problem of MS Excel. Try opening the file with another editor and you will notice that your encoding was successful already. To make MS Excel happy, move from UTF-8 to UTF-16. This should work:
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel_tab, encoding="utf-16", **kwds):
# Redirect output to a queue
self.queue = StringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
# Force BOM
if encoding=="utf-16":
import codecs
f.write(codecs.BOM_UTF16)
self.encoding = encoding
def writerow(self, row):
# Modified from original: now using unicode(s) to deal with e.g. ints
self.writer.writerow([unicode(s).encode("utf-8") for s in row])
# Fetch UTF-8 output from the queue ...
data = self.queue.getvalue()
data = data.decode("utf-8")
# ... and reencode it into the target encoding
data = data.encode(self.encoding)
# strip BOM
if self.encoding == "utf-16":
data = data[2:]
# write to the target stream
self.stream.write(data)
# empty queue
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)

I couldn't respond to Mark above, but I just made one modification which fixed the error that was caused if data in the cells was not unicode, e.g. float or int data. I replaced this line into the UnicodeWriter function: "self.writer.writerow([s.encode("utf-8") if type(s)==types.UnicodeType else s for s in row])" so that it became:
class UnicodeWriter:
def __init__(self, f, dialect=csv.excel, encoding="utf-8-sig", **kwds):
self.queue = cStringIO.StringIO()
self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
self.stream = f
self.encoder = codecs.getincrementalencoder(encoding)()
def writerow(self, row):
'''writerow(unicode) -> None
This function takes a Unicode string and encodes it to the output.
'''
self.writer.writerow([s.encode("utf-8") if type(s)==types.UnicodeType else s for s in row])
data = self.queue.getvalue()
data = data.decode("utf-8")
data = self.encoder.encode(data)
self.stream.write(data)
self.queue.truncate(0)
def writerows(self, rows):
for row in rows:
self.writerow(row)
You will also need to "import types".

I don't think this is the best answer, but it's probably the most self-contained answer and also the funniest.
UTF7 is a 7-bit ASCII encoding of unicode. It just so happens that UTF7 makes no special use of commas, quotes, or whitespace. It just passes them through from input to output. So really it makes no difference if you UTF7-encode first and then parse as CSV, or if you parse as CSV first and then UTF7-encode. Python 2's CSV parser can't handle unicode, but python 2 does have a UTF-7 encoder. So you can encode, parse, and then decode, and it's as if you had a unicode-capable parser.
import csv
import io
def read_csv(path):
with io.open(path, 'rt', encoding='utf8') as f:
lines = f.read().split("\r\n")
lines = [l.encode('utf7').decode('ascii') for l in lines]
reader = csv.reader(lines, dialect=csv.excel)
for row in reader:
yield [x.encode('ascii').decode('utf7') for x in row]
for row in read_csv("lol.csv"):
print(repr(row))
lol.csv
foo,bar,foo∆bar,"foo,bar"
output:
[u'foo', u'bar', u'foo\u2206bar', u'foo,bar']