Occurrence of Empty list in using csv module in Python 3.6

Question

This is a code in a book.

import csv
villains = [['Doctor', 'No'],
            ['Rosa', 'Klebb'],
            ['Mister', 'Big'],
            ['Auric', 'Goldfinger'],
            ['Ernst', 'Blofeld'],
            ]
with open('villains', 'wt') as fout:
    csvout = csv.writer(fout)
    csvout.writerows(villains)
with open('villains', 'rt') as fin:
    cin = csv.reader(fin)
    villains = [row for row in cin]
print(villains)

My result is

[['Doctor', 'No'], [], 
['Rosa', 'Klebb'], [], 
['Mister', 'Big'], [], 
['Auric', 'Goldfinger'], [], 
['Ernst', 'Blofeld'], []]

Expected result is

[['Doctor', 'No'], 
['Rosa', 'Klebb'], 
['Mister', 'Big', 
['Auric', 'Goldfinger'], 
['Ernst', 'Blofeld']]

But I have some empty list in my result. I don't understand why these are appearing.

MY QUESTION

What in my code makes the empty lists?
How to correct my code to obtain expected result?

Thanks in advance.

DeepSpace · Accepted Answer · 2018-01-02 11:51:33Z

2

The empty lines are there because the generated file contains empty lines:

Doctor,No

Rosa,Klebb

Mister,Big

Auric,Goldfinger

Ernst,Blofeld

This can be remedied by adding if row when reading the file:

with open('villains', 'r') as fin:
    cin = csv.reader(fin)
    villains = [row for row in cin if row]

print(villains)
#  [['Doctor', 'No'], ['Rosa', 'Klebb'], ['Mister', 'Big'], ['Auric', 'Goldfinger'],
#  ['Ernst', 'Blofeld']]

Alternatively you can generate the file without blank lines by passing newline='' to open:

with open('villains', 'wt', newline='') as fout:
    csvout = csv.writer(fout)
    csvout.writerows(villains)

edited Jan 2, 2018 at 11:51

answered Jan 2, 2018 at 10:57

DeepSpace

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1 Comment

Jeong Over a year ago

What makes empty lines in the generated file? When I check the file by notepad, there is no empty line.

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