I want to generate all possible sequence of alternative digit and numbers. For example 
5j1c6l2d4p9a9h9q
6d5m7w4c8h7z4s0i
3z0v5w1f3r6b2b1z
NumberSmallletterNumberSmallletter
NumberSmallletterNumberSmallletter
NumberSmallletterNumberSmallletter
NumberSmallletterNumberSmallletter
I can do it by using 16 loop But it will take 30+ hours (rough idea). Is there any efficient way. I hope there will be in python.
There is no "efficient" way to do this. There are 2.8242954e+19 different possible combonations, or 28,242,954,000,000,000,000. If each combination is 16 characters long, storing this all in a raw text file would take up 451,887,264,000 gigabytes, 441,296,156.25 terabytes, 430,953.2775878906 petabytes, or 420.8528101444 exabytes. The largest hard drive available to the average consumer is 16TB (Samsung PM1633a). They cost 12 thousand US dollars. This puts the total cost of storing all of this data to 330,972,117,600 US dollars (3677.46797 times Bill Gates' net worth). Even ignoring the amount of space all of these drives would take up, and ignoring the cost of the hardware you would need to connect them to, and assuming that they could all be running at highest performance all together in a lossless RAID array, this would make the write speed 330,972,118 gigabytes a second. Sounds like a lot, doesn't it? Even with that write speed, the file would take 22 minutes to write, assuming that there were no bottlenecks from CPU power, RAM speed, or the RAID controller itself. 
Sources - a calculator.
Generate all possible sequence of altrenate digits and alphabets