added flatten filter

docs/docsite/rst/playbooks_filters.rst

@@ -116,6 +116,19 @@ To get the maximum value from a list of numbers::
 
     {{ [3, 4, 2] | max }}
 
+.. versionadded:: 2.5
+
+Flatten a list (same thing the `flatten` lookup does)::
+
+    {{ [3, [4, 2] ]|flatten }}
+
+Flatten only the first level of a list (akin to the `items` lookup)::
+
+    {{ [3, [4, [2]] ]|flatten(level=1) }}
+
+
+To get the minimum value from list of numbers::
+
 .. _set_theory_filters:
 
 Set Theory Filters

lib/ansible/plugins/filter/core.py

@@ -465,13 +465,35 @@ def b64decode(string):
     return to_text(base64.b64decode(to_bytes(string, errors='surrogate_or_strict')))
 
 
+def flatten(mylist, levels=None):
+
+    ret = []
+    for element in mylist:
+        if element in (None, 'None', 'null'):
+            # ignore undefined items
+            break
+        elif isinstance(element, MutableSequence):
+            if levels is None:
+                ret.extend(flatten(element))
+            elif levels >= 1:
+                levels = int(levels) - 1
+                ret.extend(flatten(element, levels=levels))
+            else:
+                ret.append(element)
+        else:
+            ret.append(element)
+
+    return ret
+
+
 class FilterModule(object):
     ''' Ansible core jinja2 filters '''
 
     def filters(self):
         return {
             # jinja2 overrides
             'groupby': do_groupby,
+            'flatten': flatten,
 
             # base 64
             'b64decode': b64decode,

test/integration/targets/filters/tasks/main.yml

@@ -168,3 +168,20 @@
     that:
       - _bad_urlsplit_filter is failed
       - "'unknown URL component' in _bad_urlsplit_filter.msg"
+
+- name: Flatten tests
+  block:
+    - name: use flatten
+      set_fact:
+        flat_full: '{{orig_list|flatten}}'
+        flat_one: '{{orig_list|flatten(levels=1)}}'
+        flat_two: '{{orig_list|flatten(levels=2)}}'
+
+    - name: Verify flatten filter works as expected
+      assert:
+        that:
+          - flat_full == [1, 2, 3, 4, 5, 6, 7]
+          - flat_one == [1, 2, 3, [4, [5]], 6, 7]
+          - flat_two == [1, 2, 3, 4, [5], 6, 7]
+  vars:
+    orig_list: [1, 2, [3, [4, [5]], 6], 7]