CSV Module's writer won't let me write binary out

Question

I tried to just use the 'w' tag while opening the file, but it double spaced the lines which caused the read to not work. So I found that changing to 'wb' will be the correct formatting. Now that I am using the 'wb' flag I can't get the csv.writer.writerow() to work. I have encoded all my strings and am lost as to why I keep getting this error. All the questions I see say that b'string here' or myString.encode('ascii') solves the error I get, but it is not solving it for me. Here is what I have:

    dataWriter = csv.writer(open(fileName, 'wb'))
    for i in range(self.ui.table.rowCount()):
        rowData = [self.ui.table.item(i,0).text().encode('utf-8')\
        ,self.ui.table.item(i,1).text().encode('utf-8')\
        ,self.ui.table.item(i,2).text().encode('utf-8')\
        ,self.ui.table.item(i,3).text().encode('utf-8')\
        ,self.ui.table.item(i,4).text().encode('utf-8')]
        dataWriter.writerow(rowData)

Which I figured would work but it still gives me the following error: "TypeError: must be bytes or buffer, not str" on the line "dataWriter.writerow(rowData).

Any help would be apreciated. Thank you.

Answer 1

You appear to be running Python 3.x. Advice about using binary mode for csv files applies to Python 2.x. The codecs module is not required for 3.x -- just use encoding=whatever when you open the file. What is needed for 3.x is that the file be opened with newline=''. This applies to both reading and writing, although it is not documented for writing (bug report has been submitted). After sorting out your doble-spacing problem, this will work:

import csv
data = [
    ['\xfforick', 123.456],
    ['polonius', 987.564],
    ]
with open('demo.csv', 'w', newline='', encoding='utf8') as f:
    writer = csv.writer(f)
    for row in data:
        writer.writerow(row)

Contents of output file:

>>> open('demo.csv', 'rb').read()
b'\xc3\xbforick,123.456\r\npolonius,987.564\r\n'
>>>

Suggestion: give some consideration to legibility of your code ... instead of

for i in range(self.ui.table.rowCount()):
    rowData = [self.ui.table.item(i,0).text().encode('utf-8')\
    ,self.ui.table.item(i,1).text().encode('utf-8')\
    ,self.ui.table.item(i,2).text().encode('utf-8')\
    ,self.ui.table.item(i,3).text().encode('utf-8')\
    ,self.ui.table.item(i,4).text().encode('utf-8')]
    dataWriter.writerow(rowData)

try

table = self.ui.table
for i in range(table.rowCount()):
    row = [table.item(i, j).text() for j in range(5)]
    writer.writerow(row)