how to insert tab in a sequential word in python : nowadays I met a problem that I have a very large txt file which looks like following:

 - A T T A G C A
 - A AT A G C A
 - T TT AG G A
 - G T T A G C A

every character was spilt by \t,but some characters are connected,I want to add \t to these sequence. What I need is like following:

 - A T T A G C A
 - A A T A G C A
 - T T T A G C A
 - G T T A G C A

What can i do in python?and I need to fully use my memory to speed up the procession.