Redirecting stdin to a file

[candide]

How do I redirect stdin to a text file ? In C, this can be done with the
freopen() standard function, for instance

FILE *foo = freopen("in.txt", "r", stdin);


redirects stdin to the in.txt text file. Does anyone know a freopen()
Python equivalent ?

Notice that I'm not referring to shell redirection as the following
command line shows :

$ python myCode.py < in.txt

I need to hardcode the redirection inside the python source file.