serenade February 2016

Saving zip list to csv in Python

How I can write below zip list to csv file in python?

[{'date': '2015/01/01 00:00', 'v': 96.5},
 {'date': '2015/01/01 00:01', 'v': 97.0},
 {'date': '2015/01/01 00:02', 'v': 93.75},
 {'date': '2015/01/01 00:03', 'v': 96.0},
 {'date': '2015/01/01 00:04', 'v': 94.5}

I have this error:

_csv.Error: sequence expected

My code is here:

import csv
res = zip_list
csvfile = "/home/stm/PycharmProjects/isbak_trafik/example.csv"

with open(csvfile, "w") as output:
    writer = csv.writer(output, lineterminator='\n')
    writer.writerows(res)

Answers


Gerhard Hagerer February 2016

Since I find csv.DictWriter not transparent in what its doing, I would recommend doing the following:

with open(csvfile, "w") as output:
    output.write(';'.join(list(res[0].keys()))+"\n")
    [output.write(';'.join(list(map(str, r.values())))+"\n") for r in res]


Istvan February 2016

writer.writerows expects a sequence of values for writing a single row into the CSV file.

Using your original code:

import csv
res =[{'date': '2015/01/01 00:00', 'v': 96.5}, {'date': '2015/01/01 00:01', 'v': 97.0}, {'date': '2015/01/01 00:02', 'v': 93.75}, {'date': '2015/01/01 00:03', 'v': 96.0}, {'date': '2015/01/01 00:04', 'v': 94.5}]
csvfile = "example.csv"
with open(csvfile, "w") as output:
  writer = csv.writer(output, lineterminator='\n')
  for line in res:
    date = line['date']
    value = line['v']
    writer.writerow([date, value])


Martin Evans February 2016

You can switch to using Python's DictWriter for this. You can pass a list of column headers, this ensures that the order of the columns in the output is what you require. Only columns in this list are written to the your output file:

import csv

zip_list = [
    {'date': '2015/01/01 00:00', 'v': 96.5},
    {'date': '2015/01/01 00:01', 'v': 97.0},
    {'date': '2015/01/01 00:02', 'v': 93.75},
    {'date': '2015/01/01 00:03', 'v': 96.0},
    {'date': '2015/01/01 00:04', 'v': 94.5}]

csvfile = "/home/stm/PycharmProjects/isbak_trafik/example.csv"

with open(csvfile, "wb") as output:
    writer = csv.DictWriter(output, fieldnames=['date', 'v'])
    writer.writeheader()
    writer.writerows(zip_list)

This would produce the following output:

date,v
2015/01/01 00:00,96.5
2015/01/01 00:01,97.0
2015/01/01 00:02,93.75
2015/01/01 00:03,96.0
2015/01/01 00:04,94.5

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Asked in February 2016
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