Arch Linux User Repository

Why do you have python3 in makedepends but python in depends? Just use python for both.

rshell uses a source package so you can just use https:// files.pythonhosted.org/packages/source/${_name::1}/$_name/$_name-$pkgver.tar.gz in the PKGBUILDs source array.

See: https://wiki.archlinux.org/index.php/Python_package_guidelines

This would be my recommended PKGBUILD:

$ diff PKGBUILD.old PKGBUILD.new
3,4c3,7
< pkgname=rshell
< pkgver=0.0.24
---
> pkgname=python-rshell
> _name=${pkgname#python-}
> provides=(rshell)
> conflicts=(rshell)
> pkgver=0.0.26
8,9c11,12
< depends=('python' 'python-pyudev' 'python-pyserial')
< makedepends=('python3')
---
> depends=('python-pyudev' 'python-pyserial')
> makedepends=('python-setuptools')
12,13c15,16
< source=('https://files.pythonhosted.org/packages/5e/70/d48ce2329734b214d81b08b7ba048869eefafac9d5b482dbccd4f7a4dbef/rshell-0.0.24.tar.gz')
< md5sums=('6fc1bda8781d1ca77a0d1e37b58620ef')
---
> source=("https://files.pythonhosted.org/packages/source/${_name::1}/${_name}/${_name}-${pkgver}.tar.gz")
> sha256sums=('cc447a3c9853a50585d7fdd6356922e8a89debb67932e60cf241f23fbd72db16')
16c19
<     cd $srcdir/rshell-0.0.24
---
>     cd $srcdir/${_name}-${pkgver}
21,22c24,25
<     cd $srcdir/rshell-0.0.24
<     python setup.py install --root="$pkgdir" --optimize=1 
---
>     cd $srcdir/${_name}-${pkgver}
>     python setup.py install --root="${pkgdir}" --optimize=1 --skip-build

You forgot the python-udev dependency. It breaks when trying to open