Python regex split without empty string

I have the following file names that exhibit this pattern:

000014_L_20111007T084734-20111008T023142.txt
000014_U_20111007T084734-20111008T023142.txt
...

I want to extract the middle two time stamp parts after the second underscore '_' and before '.txt'. So I used the following Python regex string split:

time_info = re.split('^[0-9]+_[LU]_|-|\.txt$', f)

But this gives me two extra empty strings in the returned list:

time_info=['', '20111007T084734', '20111008T023142', '']

How do I get only the two time stamp information? i.e. I want:

time_info=['20111007T084734', '20111008T023142']