如何将数据作为字符串(而非文件)写入CSV格式?

问题:如何将数据作为字符串(而非文件)写入CSV格式?

我想将数据[1,2,'a','He said "what do you mean?"']转换为CSV格式的字符串。

通常会用到csv.writer()它,因为它处理所有疯狂的情况(逗号转义,引号转义,CSV方言等)。捕获的结果是csv.writer()期望输出到文件对象,而不是字符串。

我当前的解决方案是此功能有点怪异:

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

谁能提供一种仍然可以很好地处理边缘情况的更优雅的解决方案?

编辑:这是我最终完成的方式:

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

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')

回答 0

您可以使用StringIO而不是自己的Dummy_Writer

此模块实现了类似文件的类,该类StringIO读写字符串缓冲区(也称为内存文件)。

还有cStringIO,这是StringIO该类的更快版本。

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.


回答 1

在Python 3中:

>>> 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'

对于Python 2,需要更改一些细节:

>>> 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'

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'

回答 2

我发现答案总的来说有点令人困惑。对于Python 2,这种用法对我有用:

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)

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)

回答 3

由于我大量使用此代码将结果从sanic作为csv数据异步流回用户,因此我为Python 3编写了以下代码段。

该代码段可让您一次又一次地重复使用相同的StringIo缓冲区。


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"

例:

csv_formatter = ArgsToCsv()

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

在github gist上查看更多用法:源代码和测试

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


回答 4

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

stream = StringIO(file)

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

stream = StringIO(file)

csv_file = csv.DictReader(stream)

回答 5

这是适用于utf-8的版本。csvline2string仅用于一行,末尾没有换行符,csv2string用于多行,具有换行符:

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()

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()