#Updated dec 2020
#It will creates Text file in path directory using name of file.txt
import os

path = 'some/path/to/file.txt'
if not os.path.exists(path):
    with open(path, 'w') as f:
        f.write('Hello, world')
#==== OR ===
mode = 'a' if os.path.exists(path) else 'w'
with open(path, mode) as f:
    f.write('Hello, world!\n')