%pypi_source() %{lua:
    local src = rpm.expand('%1')
    local ver = rpm.expand('%2')
    local ext = rpm.expand('%3')
    local url = rpm.expand('%__pypi_url')
\
    -- If no first argument, try %srcname, then %pypi_name, then %name
    -- Note that rpm leaves macros unchanged if they are not defined.
    if src == '%1' then
        src = rpm.expand('%srcname')
    end
    if src == '%srcname' then
        src = rpm.expand('%pypi_name')
    end
    if src == '%pypi_name' then
        src = rpm.expand('%name')
    end
\
    -- If no second argument, use %version
    if ver == '%2' then
        ver = rpm.expand('%version')
    end
\
    -- If no third argument, use the preset default extension
    if ext == '%3' then
        ext = rpm.expand('%__pypi_default_extension')
    end
\
    local first = string.sub(src, 1, 1)
\
    print(url .. first .. '/' .. src .. '/' .. src .. '-' .. ver .. '.' .. ext)
}