apk add --no-cache curl python py-pip
 fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/main/x86_64/APKINDEX.tar.gz
 fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/community/x86_64/APKINDEX.tar.gz
 ERROR: unsatisfiable constraints:
   python (missing):
     required by: world[python]

apk add --update --no-cache curl py-pip

It will install python3 automatically with pip.

python (version 2) has been decommissioned from latest packages.