diff --git a/prometheus/libtofs.jinja b/prometheus/libtofs.jinja
index 0668925..f39fd42 100644
--- a/prometheus/libtofs.jinja
+++ b/prometheus/libtofs.jinja
@@ -1,40 +1,37 @@
-{%- macro files_switch(source_files,
-                       lookup=None,
-                       default_files_switch=['id', 'os_family'],
-                       indent_width=6,
-                       use_subpath=False) %}
-  {#-
+{%- macro files_switch(
+      source_files,
+      lookup=None,
+      default_files_switch=["id", "os_family"],
+      indent_width=6,
+      use_subpath=False
+    ) %}
+{#-
     Returns a valid value for the "source" parameter of a "file.managed"
     state function. This makes easier the usage of the Template Override and
     Files Switch (TOFS) pattern.
-
     Params:
       * source_files: ordered list of files to look for
-      * lookup: key under '<tplroot>:tofs:source_files' to prepend to the
+      * lookup: key under "<tplroot>:tofs:source_files" to prepend to the
         list of source files
       * default_files_switch: if there's no config (e.g. pillar)
-        '<tplroot>:tofs:files_switch' this is the ordered list of grains to
+        "<tplroot>:tofs:files_switch" this is the ordered list of grains to
         use as selector switch of the directories under
         "<path_prefix>/files"
       * indent_width: indentation of the result value to conform to YAML
       * use_subpath: defaults to `False` but if set, lookup the source file
         recursively from the current state directory up to `tplroot`
-
     Example (based on a `tplroot` of `xxx`):
-
     If we have a state:
-
       Deploy configuration:
         file.managed:
           - name: /etc/yyy/zzz.conf
-          - source: {{ files_switch(['/etc/yyy/zzz.conf', '/etc/yyy/zzz.conf.jinja'],
-                                    lookup='Deploy configuration'
-                    ) }}
+          - source: {{ files_switch(
+                         ["/etc/yyy/zzz.conf", "/etc/yyy/zzz.conf.jinja"],
+                         lookup="Deploy configuration",
+                       ) }}
           - template: jinja
-
     In a minion with id=theminion and os_family=RedHat, it's going to be
     rendered as:
-
       Deploy configuration:
         file.managed:
           - name: /etc/yyy/zzz.conf
@@ -46,67 +43,73 @@
             - salt://xxx/files/default/etc/yyy/zzz.conf
             - salt://xxx/files/default/etc/yyy/zzz.conf.jinja
           - template: jinja
-  #}
-  {#- Get the `tplroot` from `tpldir` #}
-  {%- set tplroot = tpldir.split('/')[0] %}
-  {%- set path_prefix = salt['config.get'](tplroot ~ ':tofs:path_prefix', tplroot) %}
-  {%- set files_dir = salt['config.get'](tplroot ~ ':tofs:dirs:files', 'files') %}
-  {%- set files_switch_list = salt['config.get'](
-      tplroot ~ ':tofs:files_switch',
-      default_files_switch
-  ) %}
-  {#- Lookup source_files (v2), files (v1), or fallback to an empty list #}
-  {%- set src_files = salt['config.get'](
-      tplroot ~ ':tofs:source_files:' ~ lookup,
-      salt['config.get'](tplroot ~ ':tofs:files:' ~ lookup, [])
-  ) %}
-  {#- Append the default source_files #}
-  {%- set src_files = src_files + source_files %}
-  {#- Only add to [''] when supporting older TOFS implementations #}
-  {%- set path_prefix_exts = [''] %}
-  {%- if use_subpath and tplroot != tpldir %}
-    {#- Walk directory tree to find {{ files_dir }} #}
-    {%- set subpath_parts = tpldir.lstrip(tplroot).lstrip('/').split('/') %}
-    {%- for path in subpath_parts %}
-      {%- set subpath = subpath_parts[0:loop.index] | join('/') %}
-      {%- do path_prefix_exts.append('/' ~ subpath) %}
-    {%- endfor %}
-  {%- endif %}
-  {%- for path_prefix_ext in path_prefix_exts|reverse %}
-    {%- set path_prefix_inc_ext = path_prefix ~ path_prefix_ext %}
-    {#- For older TOFS implementation, use `files_switch` from the config #}
-    {#- Use the default, new method otherwise #}
-    {%- set fsl = salt['config.get'](
-        tplroot ~ path_prefix_ext|replace('/', ':') ~ ':files_switch',
-        files_switch_list
-    ) %}
-    {#- Append an empty value to evaluate as `default` in the loop below #}
-    {%- if '' not in fsl %}
-      {%- set fsl = fsl + [''] %}
-    {%- endif %}
-    {%- for fs in fsl %}
-      {%- for src_file in src_files %}
-        {%- if fs %}
-          {%- set fs_dirs = salt['config.get'](fs, fs) %}
-        {%- else %}
-          {%- set fs_dirs = salt['config.get'](tplroot ~ ':tofs:dirs:default', 'default') %}
-        {%- endif %}
-        {#- Force the `config.get` lookup result as a list where necessary #}
-        {#- since we need to also handle grains that are lists #}
-        {%- if fs_dirs is string %}
-          {%- set fs_dirs = [fs_dirs] %}
-        {%- endif %}
-        {%- for fs_dir in fs_dirs %}
-          {%- set url = [
-              '- salt:/',
-              path_prefix_inc_ext.strip('/'),
-              files_dir.strip('/'),
-              fs_dir.strip('/'),
-              src_file.strip('/'),
-          ] | select | join('/') %}
+#}
+{#-   Get the `tplroot` from `tpldir` #}
+{%-   set tplroot = tpldir.split("/")[0] %}
+{%-   set path_prefix = salt["config.get"](tplroot ~ ":tofs:path_prefix", tplroot) %}
+{%-   set files_dir = salt["config.get"](tplroot ~ ":tofs:dirs:files", "files") %}
+{%-   set files_switch_list = salt["config.get"](
+        tplroot ~ ":tofs:files_switch", default_files_switch
+      ) %}
+{#-   Lookup source_files (v2), files (v1), or fallback to an empty list #}
+{%-   set src_files = salt["config.get"](
+        tplroot ~ ":tofs:source_files:" ~ lookup,
+        salt["config.get"](tplroot ~ ":tofs:files:" ~ lookup, []),
+      ) %}
+{#-   Append the default source_files #}
+{%-   set src_files = src_files + source_files %}
+{#-   Only add to [""] when supporting older TOFS implementations #}
+{%-   set path_prefix_exts = [""] %}
+{%-   if use_subpath and tplroot != tpldir %}
+{#-     Walk directory tree to find {{ files_dir }} #}
+{%-     set subpath_parts = tpldir.lstrip(tplroot).lstrip("/").split("/") %}
+{%-     for path in subpath_parts %}
+{%-       set subpath = subpath_parts[0 : loop.index] | join("/") %}
+{%-       do path_prefix_exts.append("/" ~ subpath) %}
+{%-     endfor %}
+{%-   endif %}
+{%-   for path_prefix_ext in path_prefix_exts | reverse %}
+{%-     set path_prefix_inc_ext = path_prefix ~ path_prefix_ext %}
+{#-     For older TOFS implementation, use `files_switch` from the config #}
+{#-     Use the default, new method otherwise #}
+{%-     set fsl = salt["config.get"](
+          tplroot ~ path_prefix_ext | replace("/", ":") ~ ":files_switch",
+          files_switch_list,
+        ) %}
+{#-     Append an empty value to evaluate as `default` in the loop below #}
+{%-     if "" not in fsl %}
+{%-       set fsl = fsl + [""] %}
+{%-     endif %}
+{%-     for fs in fsl %}
+{%-       for src_file in src_files %}
+{%-         if fs %}
+{%-           set fs_dirs = salt["config.get"](fs, fs) %}
+{%-         else %}
+{%-           set fs_dirs = salt["config.get"](
+                tplroot ~ ":tofs:dirs:default", "default"
+              ) %}
+{%-         endif %}
+{#-         Force the `config.get` lookup result as a list where necessary #}
+{#-         since we need to also handle grains that are lists #}
+{%-         if fs_dirs is string %}
+{%-           set fs_dirs = [fs_dirs] %}
+{%-         endif %}
+{%-         for fs_dir in fs_dirs %}
+{#-           strip empty elements by using a select #}
+{%-           set url = (
+                [
+                  "- salt:/",
+                  path_prefix_inc_ext.strip("/"),
+                  files_dir.strip("/"),
+                  fs_dir.strip("/"),
+                  src_file.strip("/"),
+                ]
+                | select
+                | join("/")
+              ) %}
 {{ url | indent(indent_width, true) }}
-        {%- endfor %}
-      {%- endfor %}
-    {%- endfor %}
-  {%- endfor %}
+{%-         endfor %}
+{%-       endfor %}
+{%-     endfor %}
+{%-   endfor %}
 {%- endmacro %}