There are many languages that have "eval" and yet have unambiguous parse trees for the actual code of the program (as opposed to the code evaluated at runtime).
in reply to Re^2: Perl Cannot Be Parsed: A Formal Proof
in thread Perl Cannot Be Parsed: A Formal Proof
If you run this Python program you'll see it prints out a complete parse tree of the program BEFORE it runs eval. Before you jump down my throat, I'm not saying that this makes Python a better language than Perl. It's just a fact that a language can be constructed so that "eval" is totally handled at runtime and does not affect the parsability of the program.
To bring this back to the original post, the "parser" module is the Python equivalent of what Parse::Perl would be if Perl parsing were possible.
x = eval(sys.stdin.readline())
print "yes", x
print "no", x