While the string method works pretty well, I do not think this is the best way. If 98% of multiline string will need deindenting, it is better to do it by default. For those 2% that do not need deintentation, it can be prohibited by adding the backslash followed by a newline at first position (except the start of the string). For example:
smile = '''\
XX
XX X
X
XXX X
X
XX X
XX
\
'''
Yes, this is breaking change. But we have import from __future__ and FutureWarning. The plan may be:
3.9. Implement "from __future__ import deindent".
3.11. Emit a FutureWarning for multiline literals that will be changed by dedending if "from __future__ import deindent" is not specified.
3.13. Make it the default behavior.