Python3 write and read from CSV integer to string

Question

I've spent a few hours staring at this and I can't figure it out. I'm sure it's basic but would be great of you could kindly help me out.

I have a list named "export_data" that contains other lists, and integers. For example.

print(type(export_data[0]))
print(type(export_data[5]))

#Output is: <class 'list'>
<class 'int'>

I then write the "export_data" to a csv file. However, When I subsequently read the file and extract a column value it comes back as a string. So now I have a "[1,2,3]" that I'm unsure how to convert back to a list.

with open('record ' + str(current) + '.csv', 'a', newline='') as f:
    writer = csv.writer(f)

    writer.writerow(export_data)
    del writer
    f.close()

with open('record Wednesday,Apr:29.csv', 'r') as rf:
    reader = csv.reader(rf)
    for i in reader:
        (group_a.append(i[1]))
        (x.append(i[0]))
        (hr.append(i[5]))

print(type(export_data[0]))
print(type(export_data[5]))
#Output: <class 'str'>
<class 'str'>

I'm using the data from the csv file to plot the data in DASH using plotly. Therefore I can't enter a list for my x and y values. Thanks for your help.

CSV will only ever return you text - its a text based format aftet all. — Patrick Artner, Apr 30 '20 at 07:05

Thaer A · Accepted Answer · 2020-04-30T07:23:32.683

0

To convert "[1,2,3]" back to a list use eval() or ast.literal_eval as Patrick Artner mentioned (Note: eval is not a good practice and it's not safe, see comments. Still I use it in quick local scripting if I'm certain that the input data is safe) :

lst_str = eval("[1,2,3]")
print(lst_str)
print(type(lst_str))

===

import ast

lst_str = ast.literal_eval("[1,2,3]")
print(lst_str)
print(type(lst_str))

Output:

[1, 2, 3]
<class 'list'>

edited Apr 30 '20 at 07:23

answered Apr 30 '20 at 07:05

Thaer A

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Dont use eval, its bad practice. – Albin Paul Apr 30 '20 at 07:08
@PatrickArtner is it safer? – Thaer A Apr 30 '20 at 07:10
@AlbinPaul What's a better alternative? Parsing the string? – Thaer A Apr 30 '20 at 07:11
1

[using-pythons-eval-vs-ast-literal-eval](https://stackoverflow.com/questions/15197673/using-pythons-eval-vs-ast-literal-eval) – Patrick Artner Apr 30 '20 at 07:12
1

[eval_really_is_dangerous.html](https://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html) – Patrick Artner Apr 30 '20 at 07:13

Python3 write and read from CSV integer to string

1 Answers1