Question

Here’s the entirety of my code:

import csv

def numbersOut():
    for i in range (1, 1001):
        out.writerow("%s" % (i+1, ))
        out.writerow("\n")

csvname = raw_input("Enter desired filename: ")
headers = ["ID", "Student", "Grade"]

out = csv.writer(open(csvname + ".csv","w"), delimiter=',', lineterminator='\n', quoting=csv.QUOTE_ALL)
out.writerow(headers)
out.writerow(numbersOut())

And the section that’s throwing up the “sequence expected” error is line 14, namely this one: out.writerow(numbersOut())

Basically, what I’m trying to do is use the function numbersOut() to put 1000 rows in a CSV file, each with it’s own ID (Line 1 (Minus headers) will = 1, Line 2 will = 2, etc). I managed to get them all on one row by using range, but that’s not what I’m needed.

However, I keep getting an error when trying to use my function. I’m not sure if it’s a problem with how I’m calling it or whether it’s a problem within the function itself.

Any ideas? If anything needs clarifying, please ask; I have a habit of not making much sense.

Thanks in advance!

EDIT: Traceback, as requested:

Traceback (most recent call last):
  File "writer.py", line 14, in <module>
   out.writerow(numbersOut())
_csv.Error: sequence expected

Answer 1

In Python, if a function falls off the end without returning, it is assumed to return None. Your numbersOut() function doesn’t return anything. So, when you write

out.writerow(numbersOut())

you end up calling out.writerow(None). This will give you the error you’re seeing, as None isn’t a sequence and the csv module doesn’t know how to write out None as a row of CSV data.

I think you would be better off declaring numbersOut to take out as an argument:

def numbersOut(out):
    for i in range (1, 1001):
        out.writerow("%s" % (i+1, ))
        out.writerow("\n")

and then call it using

numbersOut(out)

---

There are another couple of changes I’d recommend making.

If you only want to write a single value to a row, replace the line

        out.writerow("%s" % (i+1, ))

with

        out.writerow(["%s" % (i+1, )])

(note the inserted [ and ]).
writerow takes a sequence of values and writes each value out into a separate comma-separated cell. If you pass a single string, that gets interpreted as a sequence of characters, and each character ends up in its own cell.

Secondly, I’d recommend removing the line out.writerow("\n"). When you write a row using writerow, the csv module will output the end-of-line for you. There’s no need for you to end the lines manually. In fact, the line out.writerow("\n") ends up writing a cell containing a newline between each row that contains a number.