CODEWITHSUNDEEP
pythonstringcsv
Li-aung Yip
Li-aung Yip

Reputation: 12486

How do I write data into CSV format as string (not file)?

I want to cast data like [1,2,'a','He said "what do you mean?"'] to a CSV-formatted string.

Normally one would use csv.writer() for this, because it handles all the crazy edge cases (comma escaping, quote mark escaping, CSV dialects, etc.) The catch is that csv.writer() expects to output to a file object, not to a string.

My current solution is this somewhat hacky function:

def CSV_String_Writeline(data):
    class Dummy_Writer:
        def write(self,instring):
            self.outstring = instring.strip("\r\n")
    dw = Dummy_Writer()
    csv_w = csv.writer( dw )
    csv_w.writerow(data)
    return dw.outstring

Can anyone give a more elegant solution that still handles the edge cases well?

Edit: Here's how I ended up doing it:

def csv2string(data):
    si = StringIO.StringIO()
    cw = csv.writer(si)
    cw.writerow(data)
    return si.getvalue().strip('\r\n')

Upvotes: 177

Views: 169241

Answers (7)

Johannes valbjørn
Johannes valbjørn

Reputation: 408

since i use this quite a lot to stream results asynchronously from sanic back to the user as csv data i wrote the following snippet for Python 3.

The snippet lets you reuse the same StringIo buffer over and over again.

import csv
from io import StringIO


class ArgsToCsv:
    def __init__(self, seperator=","):
        self.seperator = seperator
        self.buffer = StringIO()
        self.writer = csv.writer(self.buffer)

    def stringify(self, *args):
        self.writer.writerow(args)
        value = self.buffer.getvalue().strip("\r\n")
        self.buffer.seek(0)
        self.buffer.truncate(0)
        return value + "\n"

example:

csv_formatter = ArgsToCsv()

output += csv_formatter.stringify(
    10,
    """
    lol i have some pretty
    "freaky"
    strings right here \' yo!
    """,
    [10, 20, 30],
)

Check out further usage at the github gist: source and test

Upvotes: 9

alex
alex

Reputation: 955

i adopt the answer of @user2099484 above, with a small amendment for unicode

import csv, io

def csv2string(data):
    si = io.BytesIO()
    cw = csv.writer(si)
    data = [f.encode('utf-8') if type(f) == unicode else f for f in data]
    cw.writerow(data)
    return si.getvalue().strip('\r\n')

data=[1,2,'a','He said "what do you mean?"']
print csv2string(data)
data2=[1,2,u'שלום','He said "what do you mean?"']
print csv2string(data2)

Upvotes: 1

NPE
NPE

Reputation: 500903

You could use StringIO instead of your own Dummy_Writer:

This module implements a file-like class, StringIO, that reads and writes a string buffer (also known as memory files).

There is also cStringIO, which is a faster version of the StringIO class.

Upvotes: 73

user2099484
user2099484

Reputation: 4559

I found the answers, all in all, a bit confusing. For Python 2, this usage worked for me:

import csv, io

def csv2string(data):
    si = io.BytesIO()
    cw = csv.writer(si)
    cw.writerow(data)
    return si.getvalue().strip('\r\n')

data=[1,2,'a','He said "what do you mean?"']
print csv2string(data)

Upvotes: 7

Humberto Arocha
Humberto Arocha

Reputation: 17

import csv
from StringIO import StringIO
with open('file.csv') as file:
    file = file.read()

stream = StringIO(file)

csv_file = csv.DictReader(stream)

Upvotes: -2

bjelli
bjelli

Reputation: 10100

Here's the version that works for utf-8. csvline2string for just one line, without linebreaks at the end, csv2string for many lines, with linebreaks:

import csv, io

def csvline2string(one_line_of_data):
    si = BytesIO.StringIO()
    cw = csv.writer(si)
    cw.writerow(one_line_of_data)
    return si.getvalue().strip('\r\n')

def csv2string(data):
    si = BytesIO.StringIO()
    cw = csv.writer(si)
    for one_line_of_data in data:
        cw.writerow(one_line_of_data)
    return si.getvalue()

Upvotes: 0

Tim Pietzcker
Tim Pietzcker

Reputation: 336478

In Python 3:

>>> import io
>>> import csv
>>> output = io.StringIO()
>>> csvdata = [1,2,'a','He said "what do you mean?"',"Whoa!\nNewlines!"]
>>> writer = csv.writer(output, quoting=csv.QUOTE_NONNUMERIC)
>>> writer.writerow(csvdata)
59
>>> output.getvalue()
'1,2,"a","He said ""what do you mean?""","Whoa!\nNewlines!"\r\n'

Some details need to be changed a bit for Python 2:

>>> output = io.BytesIO()
>>> writer = csv.writer(output)
>>> writer.writerow(csvdata)
57L
>>> output.getvalue()
'1,2,a,"He said ""what do you mean?""","Whoa!\nNewlines!"\r\n'

Upvotes: 268

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