For Saltstack with jinja rendering: deep merge a dictionary into a first one

Jinja2 saltstack: dictionary merging

{%- macro deep_merge(a, b) %}
{%-     for k,v in b.iteritems() %}
{%-         if v is string or v is number %}
{%-             do a.update({ k: v }) %}
{%-         elif v is not mapping %}
{%-             if a[k] is not defined %}
{%-                 do a.update({ k: v }) %}
{%-             elif a[k] is iterable and a[k] is not mapping and a[k] is not string %}
{%-                 do a.update({ k: v|list + a[k]|list}) %}
{%-             else %}
{%-                 do a.update({ k: v }) %}
{%-             endif %}
{%-         elif v is mapping %}
{%-             if a[k] is not defined %}
{%-                 do a.update({ k: v }) %}
{%-             elif a[k] is not mapping %}
{%-                 do a.update({ k: v }) %}
{%-             else %}
{%-                 do deep_merge(a[k], v) %}
{%-             endif %}
{%-         else %}
{%-            do a.update({ k: 'ERROR: case not contempled in merging!' }) %}
{%-         endif %}
{%-     endfor %}
{%- endmacro %}