Under Linux and MacOS (no others tested), if "foo.py" is a DOS/
Windows style Python file (CR/LF line endings), then

  python foo.py

will work, as will

  execfile("foo.py")

and

  exec file("foo.py")

from inside Python. However,

   exec file("foo.py").read()

will report a syntax error. In other words, the parser seems to 
accept CR/LF only if the source of the data is a file, not a string.

When running under Linux and MacOS (no others tested), the exec 
statement reports a syntax error. I didn't find anything about this 
in the documentation, so I don't know if it's a bug or a feature. If 
it's a feature, it is not a useful one!