Error when adding a new column to pandas dataframe

Question

I am trying to modify .csv files in a folder. The files contain flight information from years 2011-2016.

However, year information cannot be found in the values.

I would like to solve this by using the filename of the .csv file which contains the year. I am adding a new 'year' column after reading it into a pandas dataframe. I will then export the modified file to a new .csv with only the year as its filename.

However, I am encountering this error:

ValueError:Length of values does not match length of index

Code below for your reference.

import pandas as pd
import glob
import re
import os

path = r'data_caap/'                   
all_files = glob.glob(os.path.join(path, "*.csv"))


for f in all_files:
    df = pd.read_csv(f)
    year= re.findall(r'\d{4}', f)

    #Error here
    df['year']=year
    #Error here

    df.to_csv(year)

['2001'] ['2002'] ['2003'] ['2004'] ['2005'] ['2006'] ['2007'] ['2008'] ['2009'] ['2010'] ['2011'] ['2012'] ['2013'] ['2014'] ['2015'] ['2016'] — Emman D.
– Emman D., Commented Jun 2, 2018 at 5:45

Emman D. · Accepted Answer · 2018-06-02 05:52:40Z

1

Found the cause of the error.

Must be df['year']=year[0]. findall returns a list. – DyZ

Thanks a lot @Dyz

answered Jun 2, 2018 at 5:52

Emman D.

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