import re
texts = ['config.hello.world','config.hello','config.hello','config.hello.world']
rx = re.compile(r'\bconfig\.([\w.]+)(?![(\w])')
for text in texts:
m = rx.search(text)
if m:
print(text + " => " + m.group(1))
else:
print(text + " => NO MATCH")
aW1wb3J0IHJlCnRleHRzID0gWydjb25maWcuaGVsbG8ud29ybGQnLCdjb25maWcuaGVsbG8nLCdjb25maWcuaGVsbG8nLCdjb25maWcuaGVsbG8ud29ybGQnXQpyeCA9IHJlLmNvbXBpbGUocidcYmNvbmZpZ1wuKFtcdy5dKykoPyFbKFx3XSknKQpmb3IgdGV4dCBpbiB0ZXh0czoKCW0gPSByeC5zZWFyY2godGV4dCkKCWlmIG06CgkJcHJpbnQodGV4dCArICIgPT4gIiArIG0uZ3JvdXAoMSkpCgllbHNlOgoJCXByaW50KHRleHQgKyAiID0+IE5PIE1BVENIIik=