Is there any python 3 command similar to the perl/php fopen command?

Yes sir it helped a lot!
Also do you have to use the hexidecimal form of the number and/or letter when writting an buffer overflow. Here's my script so far in python...

MyFile=(what do I put here the letter A or hexidecimal of A)×3000
open(MyFile)

ps. this is in python 3

You can do either. For example:

buff = "A" * 1000

is the same thing as

buff = "\x41" * 1000

Just depends on what looks nice to you...