pandas merge all csv in a folder

import glob, os    
import pandas as pd
df = pd.concat(map(pd.read_csv, glob.glob(os.path.join('', "*.csv"))))

import os
import glob
import pandas as pd
os.chdir("/mydir")

extension = 'csv'
all_filenames = [i for i in glob.glob('*.{}'.format(extension))]

#combine all files in the list
combined_csv = pd.concat([pd.read_csv(f) for f in all_filenames ])
#export to csv
combined_csv.to_csv( "combined_csv.csv", index=False, encoding='utf-8-sig')