Python - Concatenate CSV files in a specific directory

Question

I am trying to concatenate CSV files from a folder in my desktop:

C:\\Users\\Vincentc\\Desktop\\W1 

and output the final CSV to:

C:\\Users\\Vincentc\\Desktop\\W2\\conca.csv

The CSV files don't have header. However, nothing come out when I run my script, and no error message. I'm a beginner, can someone have a look at my code below, Thanks a lot!

import os
import glob
import pandas

def concatenate(indir="C:\\Users\\Vincentc\\Desktop\\W1",outfile="C:\\Users\\Vincentc\\Desktop\\W2\\conca.csv"):
    os.chdir(indir)
    fileList=glob.glob("indir")
    dfList=[]
    for filename in fileList:
        print(filename)
        df=pandas.read_csv(filename,header=None)
        dfList.append(df)
    concaDf=pandas.concat(dfList,axis=0)
    concaDf.to_csv(outfile,index=None)

Answer 1

Loading csv files into pandas only for concatenation purposes is inefficient. See this answer for a more direct alternative.

If you insist on using pandas, the 3rd party library dask provides an intuitive interface:

import dask.dataframe as dd

df = dd.read_csv('*.csv')  # read all csv files in directory lazily
df.compute().to_csv('out.csv', index=False)  # convert to pandas and save as csv

Answer 2

glob.glob() needs a wildcard to match all the files in the folder you have given. Without it, you might just get the folder name returned, and none of the files inside it. Try the following:

import os
import glob
import pandas

def concatenate(indir=r"C:\Users\Vincentc\Desktop\W1\*", outfile=r"C:\Users\Vincentc\Desktop\W2\conca.csv"):
    os.chdir(indir)
    fileList = glob.glob(indir)
    dfList = []

    for filename in fileList:
        print(filename)
        df = pandas.read_csv(filename, header=None)
        dfList.append(df)

    concaDf = pandas.concat(dfList, axis=0)
    concaDf.to_csv(outfile, index=None)

Also you can avoid the need for adding \\ by either using / or by prefixing the strings with r. This has the effect of disabling the backslash escaping on the string.