Are newlines sometimes required at end of Python code?

[Edward C. Jones]

Why does this piece of code work:

s~=~"""for~i~in~range(3):\n~~~~x~=~i\n"""
exec~s

while this one doesn't:

s~=~"""for~i~in~range(3):\n~~~~x~=~i"""
exec~s

I have replaced all the spaces in the code by "~".