#It doesn't have to be the current directory you can list them in any path you want:
path = '/some/path/to/file'
for filename in glob.glob(os.path.join(path, '*.txt')):
with open(os.path.join(os.getcwd(), filename), 'r') as f: # open in readonly mode
# do your stuff
import glob
for filename in glob.glob('*.txt'):
with open(os.path.join(os.getcwd(), filename), 'r') as f: # open in readonly mode
# do your stuff
import os
for filename in os.listdir(os.getcwd()):
with open(os.path.join(os.getcwd(), filename), 'r') as f: # open in readonly mode
# do your stuff