如何用Python合并CSV字符串中的字段？

Question

我想用Python把CSV文件中每一行的三个字段合并起来。这本来很简单，但有些字段是用双引号括起来的，而且里面还包含逗号。下面是一个例子：

,,Joe,Smith,New Haven,CT,"Moved from Portland, CT",,goo,

有没有什么简单的方法可以把每一行的第7到第9个字段合并起来呢？并不是所有的行都有用双引号括起来的逗号。

谢谢。

Answer 1

在Python中，有一个内置模块可以用来解析CSV文件：

http://docs.python.org/library/csv.html

Answer 2

你可以使用csv模块来处理这些复杂的操作：http://docs.python.org/library/csv.html

你没有具体说明你想怎么合并这些列；我想你不希望合并后的内容是“从波特兰搬到CTgoo”。下面的代码可以让你指定一个分隔符（比如", "），并且能够处理空白字段。

[transcript of session]
prompt>type merge.py
import csv

def merge_csv_cols(infile, outfile, startcol, numcols, sep=", "):
    reader = csv.reader(open(infile, "rb"))
    writer = csv.writer(open(outfile, "wb"))
    endcol = startcol + numcols
    for row in reader:
        merged = sep.join(x for x in row[startcol:endcol] if x.strip())
        row[startcol:endcol] = [merged]
        writer.writerow(row)

if __name__ == "__main__":
    import sys
    args = sys.argv[1:6]
    args[2:4] = map(int, args[2:4])
    merge_csv_cols(*args)

prompt>type input.csv
1,2,3,4,5,6,7,8,9,a,b,c
1,2,3,4,5,6,,,,a,b,c
1,2,3,4,5,6,7,8,,a,b,c
1,2,3,4,5,6,7,,9,a,b,c

prompt>\python26\python merge.py input.csv output.csv 6 3 ", "

prompt>type output.csv
1,2,3,4,5,6,"7, 8, 9",a,b,c
1,2,3,4,5,6,,a,b,c
1,2,3,4,5,6,"7, 8",a,b,c
1,2,3,4,5,6,"7, 9",a,b,c

Answer 3

像这样吗？

import csv
source= csv.reader( open("some file","rb") )
dest= csv.writer( open("another file","wb") )
for row in source:
    result= row[:6] + [ row[6]+row[7]+row[8] ] + row[9:]
    dest.writerow( result )

---

示例

>>> data=''',,Joe,Smith,New Haven,CT,"Moved from Portland, CT",,goo,
... '''.splitlines()
>>> rdr= csv.reader( data )
>>> row= rdr.next()
>>> row
['', '', 'Joe', 'Smith', 'New Haven', 'CT', 'Moved from Portland, CT', '', 'goo', '' ]
>>> row[:6] + [ row[6]+row[7]+row[8] ] +  row[9:]
['', '', 'Joe', 'Smith', 'New Haven', 'CT', 'Moved from Portland, CTgoo', '']