Python, csv writer function

Question

I created a csv function that should ask for a file path and for X number of strings to write to the file with an specified csv delimiter.

def WRITE_csv(csv_path,*args):
    with open(csv_path, "ab") as f:
        csv_list=csv.writer(f,delimiter='|')

        csv_string=""
        for arg in args:
            csv_string=csv_string+","+arg

        csv_string=csv_string[1:]

        csv_list.writerow([csv_string])

The problem is that the csv module is writing , instead of |

As a bonnus, I wanted to replace:

        csv_string=""
        for arg in args:
            csv_string=csv_string+","+arg

With a one-line function

csv_string="".format(','.join(arg for arg in args))

but it always giving me an empty string!

@Jongware: yet the delimiter argument lets you specify your own delimiter. Provided you actually use more than one column... — Martijn Pieters
– Martijn Pieters, Commented Aug 1, 2014 at 17:12
@rsm: but why are you then joining the args into a single string with commas? You appear to misunderstand how the writer works, you pass in a sequence of columns, not one string. — Martijn Pieters
– Martijn Pieters, Commented Aug 1, 2014 at 17:14
@Martijn Pieters i was wrinting a single string with commas because i noticed that when i write using writerow, i have to use the following format csv_list.writerow([string1,string2,string3,ect..]) — user3672754
– user3672754, Commented Aug 1, 2014 at 17:17
that's because you are then building a new list object. The , commas are not string values, they are Python syntax to delimit the different elements that you are asking Python to put into the list. — Martijn Pieters
– Martijn Pieters, Commented Aug 1, 2014 at 17:22

Martijn Pieters · Accepted Answer · 2014-08-01 17:24:10Z

3

You are confusing the literal , string in your value for the delimiter. You are writing just one column:

csv_list.writerow([csv_string])

so the csv.writer() never has cause to put the | delimiter in, as there is no second column to delimit. You passed in one whole string, csv_string, as a one-value list, so naturally that is seen as the only column. The module does not split the string on commas again.

Leave putting in the delimiter to the writer instead:

def WRITE_csv(csv_path, *args):
    with open(csv_path, "ab") as f:
        csv_list=csv.writer(f,delimiter='|')    
        csv_list.writerow(args)

In other words, args is already the right type for the csv.writerow() call, you don't need to convert it here.

edited Aug 1, 2014 at 17:24

answered Aug 1, 2014 at 17:11

Martijn Pieters

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