Question

I have finally switched from % to the .format() string formatting operator in my 2.x code in order to make it easier to migrate to 3.x in future. It was a bit surprising to find out that not only the %-style formatting remains in Py3, but it is widely used in the standard library code. It seems logical, because writing '(%s)' % variable is a bit shorter and maybe easier to comprehend than '({})'.format(variable). But I’m still in doubt. Is it proper (pythonic?) to use both approaches in the code?
Thank you.

Answer 1

Python 3.2 documentation said that, % will eventually go away.

http://docs.python.org/3.2/tutorial/inputoutput.html#old-string-formatting

Since str.format() is quite new, a lot of Python code still uses the %
operator. However, because this old style of formatting will
eventually be removed from the language, str.format() should generally
be used.

But as @regilero says, the sentence is gone from 3.3, which might suggest it’s not actually the case. There are some conversations here that suggest the same thing.

As of Python 3.4 the paragraph 7.1.1 reads:

The % operator can also be used for string formatting. It interprets
the left argument much like a sprintf()-style format string to be
applied to the right argument, and returns the string resulting from
this formatting operation.

See also Python 3.4 4.7.2 printf-style String Formatting.