finding a regular expression in a file

[S.B]

Hello friends.

Newb question here.
I'm trying to find an efficient way to "grep" a file with python.
The problem is that all the solutions I find on the web read a line at a time from the file with a "for line in" loop and check each line for the RE instead of sweeping through the entire file.
This looks terribly inefficient...

I can read the entire file like so:
open("/etc/passwd").read() 
and use that in an re.search - e.g:
re.search("root",open("/etc/passwd").read())
The above will work BUT it will not interpolate the "\n" as a newline and will just print the entire file as a long line.
So if I try to look for '^root' (line starting with root) instead of 'root' it will NOT work

any ideas on how to get around this?

Thanks.