pep8 fixes in arithmetic.py
pep8 fixes in arithmetic.py

hoffmabc/OpenBazaar,bankonme/OpenBazaar,bankonme/OpenBazaar,tortxof/OpenBazaar,STRML/OpenBazaar,im0rtel/OpenBazaar,hoffmabc/OpenBazaar,STRML/OpenBazaar,dionyziz/OpenBazaar,im0rtel/OpenBazaar,freebazaar/FreeBazaar,blakejakopovic/OpenBazaar,atsuyim/OpenBazaar,dionyziz/OpenBazaar,rllola/OpenBazaar,dlcorporation/openbazaar,mirrax/OpenBazaar,rllola/OpenBazaar,must-/OpenBazaar,matiasbastos/OpenBazaar,mirrax/OpenBazaar,NolanZhao/OpenBazaar,atsuyim/OpenBazaar,akhavr/OpenBazaar,hoffmabc/OpenBazaar,bankonme/OpenBazaar,dlcorporation/openbazaar,saltduck/OpenBazaar,STRML/OpenBazaar,tortxof/OpenBazaar,habibmasuro/OpenBazaar,dlcorporation/openbazaar,rllola/OpenBazaar,bankonme/OpenBazaar,Renelvon/OpenBazaar,hoffmabc/OpenBazaar,kordless/OpenBazaar,NolanZhao/OpenBazaar,akhavr/OpenBazaar,dlcorporation/openbazaar,dionyziz/OpenBazaar,saltduck/OpenBazaar,Renelvon/OpenBazaar,mirrax/OpenBazaar,im0rtel/OpenBazaar,blakejakopovic/OpenBazaar,yagoulas/OpenBazaar,hoffmabc/OpenBazaar,NolanZhao/OpenBazaar,yagoulas/OpenBazaar,dionyziz/OpenBazaar,kordless/OpenBazaar,Renelvon/OpenBazaar,saltduck/OpenBazaar,blakejakopovic/OpenBazaar,must-/OpenBazaar,yagoulas/OpenBazaar,im0rtel/OpenBazaar,rllola/OpenBazaar,freebazaar/FreeBazaar,habibmasuro/OpenBazaar,akhavr/OpenBazaar,akhavr/OpenBazaar,blakejakopovic/OpenBazaar,STRML/OpenBazaar,freebazaar/FreeBazaar,tortxof/OpenBazaar,dlcorporation/openbazaar,bglassy/OpenBazaar,saltduck/OpenBazaar,matiasbastos/OpenBazaar,must-/OpenBazaar,dlcorporation/openbazaar,yagoulas/OpenBazaar,dionyziz/OpenBazaar,kordless/OpenBazaar,bglassy/OpenBazaar,freebazaar/FreeBazaar,atsuyim/OpenBazaar,freebazaar/FreeBazaar,kordless/OpenBazaar,matiasbastos/OpenBazaar,bglassy/OpenBazaar,matiasbastos/OpenBazaar,atsuyim/OpenBazaar,hoffmabc/OpenBazaar,mirrax/OpenBazaar,tortxof/OpenBazaar,Renelvon/OpenBazaar,bglassy/OpenBazaar,akhavr/OpenBazaar,habibmasuro/OpenBazaar,habibmasuro/OpenBazaar,must-/OpenBazaar,NolanZhao/OpenBazaar