Comment # 4 on bug 1077230 from Dominique Leuenberger

I verified, libexpat-devel should be cheap enough to be buildrequired by
python3-base

The changed build tree for python3-base would be:

> diff <(osc buildinfo openSUSE:Factory python3-base standard x86_64) <(osc buildinfo openSUSE:Factory python3-base standard x86_64 -x libexpat-devel)
151a152
>   <bdep name="libexpat-devel" notmeta="1" version="2.2.5" release="1.1" arch="x86_64" project="openSUSE:Factory" repository="standard" />
160a162
>   <bdep name="libexpat1" notmeta="1" version="2.2.5" release="1.1" arch="x86_64" project="openSUSE:Factory" repository="standard" />
164d165
<   <bdep name="libexpat1" notmeta="1" version="2.2.5" release="1.1"
arch="x86_64" project="openSUSE:Factory" repository="standard" />

so in fact not really different, since python3-base already pulls in libexpat1
anyway, which means expat must have built by the time python3-base builds.