Because `.format()` is a method on an instantiated `str` object in e and so must return the same type so additional str methods could be stacked on after it, like `.format(u'hi').decode()`. Whereas the % string interpolation is a binary operation, so, like addition, where the more general type can be used for the return value, analogous to `1 + 2.0` returning a float.

--Hobson

(503) 974-6274

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On Wed, May 17, 2017 at 2:41 PM, Craig Rodrigues <rodrigc@crodrigues.org> wrote:

Hi,

While cleaning up some code during Python 2 -> Python 3 porting,
I switched some code to use str.format(), I found this behavor:

Python 2.7
=========
a = "%s" % "hi"
b = "%s" % u"hi"
c = u"%s" % "hi"
d = "{}".format("hi")
e = "{}".format(u"hi")
f = u"{}".format("hi")

type(a) == str
type(b) == unicode
type(c) == unicode
type(d) == str
type(e) == str
type(f) == unicode

My intuition would lead me to believe that type(b)
and type(e) would be the same (unicode), but they are not.
The confusion for me is why is type(e) of type str, and not unicode?

Can someone clarify this for me?

I understand that in Python 3, all these cases are str, so it is not
as big a problem there, but I am trying to keep things working on
Python 2.7.

Thanks.
--
Craig

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