Add items2dict filter that is the reverse of dict2items (#42071)

* Add items2dict filter that is the reverse of dict2items

* Address feedback about type checking, and add docs for zip/zip_longest

docs/docsite/rst/user_guide/playbooks_filters.rst

@@ -184,6 +184,77 @@ into::
     - key: Environment
       value: dev
 
+items2dict filter
+`````````````````
+
+.. versionadded:: 2.7
+
+This filter turns a list of dicts with 2 keys, into a dict, mapping the values of those keys into ``key: value`` pairs::
+
+    {{ tags | items2dict }}
+
+Which turns::
+
+    tags:
+      - key: Application
+        value: payment
+      - key: Environment
+        value: dev
+
+into::
+
+    Application: payment
+    Environment: dev
+
+This is the reverse of the ``dict2items`` filter.
+
+``items2dict`` accepts 2 keyword arguments, ``key_name`` and ``value_name`` that allow configuration of the names of the keys to use for the transformation::
+
+    {{ tags | items2dict(key_name='key', value_name='value') }}
+
+
+.. _zip_filter:
+
+zip and zip_longest filters
+```````````````````````````
+
+.. versionadded:: 2.3
+
+To get a list combining the elements of other lists use ``zip``::
+
+    - name: give me list combo of two lists
+      debug:
+       msg: "{{ [1,2,3,4,5]|zip(['a','b','c','d','e','f'])|list }}"
+
+    - name: give me shortest combo of two lists
+      debug:
+        msg: "{{ [1,2,3]|zip(['a','b','c','d','e','f'])|list }}"
+
+To always exhaust all list use ``zip_longest``::
+
+    - name: give me longest combo of three lists , fill with X
+      debug:
+        msg: "{{ [1,2,3]|zip_longest(['a','b','c','d','e','f'], [21, 22, 23], fillvalue='X')|list }}"
+
+
+Similarly to the output of the ``items2dict`` filter mentioned above, these filters can be used to contruct a ``dict``::
+
+    {{ dict(keys_list | zip(values_list)) }}
+
+Which turns::
+
+    list_one:
+      - one
+      - two
+    list_two:
+      - apple
+      - orange
+
+into::
+
+    one: apple
+    two: orange
+
 subelements Filter
 ``````````````````
 
@@ -1074,22 +1145,7 @@ Combinations always require a set size::
         msg: "{{ [1,2,3,4,5]|combinations(2)|list }}"
 
 
-To get a list combining the elements of other lists use ``zip``::
-
-    - name: give me list combo of two lists
-      debug:
-       msg: "{{ [1,2,3,4,5]|zip(['a','b','c','d','e','f'])|list }}"
-
-    - name: give me shortest combo of two lists
-      debug:
-        msg: "{{ [1,2,3]|zip(['a','b','c','d','e','f'])|list }}"
-
-To always exhaust all list use ``zip_longest``::
-
-    - name: give me longest combo of three lists , fill with X
-      debug:
-        msg: "{{ [1,2,3]|zip_longest(['a','b','c','d','e','f'], [21, 22, 23], fillvalue='X')|list }}"
-
+Also see the :ref:`zip_filter`
 
 .. versionadded:: 2.4
 

lib/ansible/plugins/filter/core.py

@@ -51,6 +51,7 @@ from ansible.errors import AnsibleFilterError
 from ansible.module_utils.six import iteritems, string_types, integer_types
 from ansible.module_utils.six.moves import reduce, shlex_quote
 from ansible.module_utils._text import to_bytes, to_text
+from ansible.module_utils.common.collections import is_sequence
 from ansible.parsing.ajson import AnsibleJSONEncoder
 from ansible.parsing.yaml.dumper import AnsibleDumper
 from ansible.utils.hashing import md5s, checksum_s
@@ -532,6 +533,16 @@ def dict_to_list_of_dict_key_value_elements(mydict):
     return ret
 
 
+def list_of_dict_key_value_elements_to_dict(mylist, key_name='key', value_name='value'):
+    ''' takes a list of dicts with each having a 'key' and 'value' keys, and transforms the list into a dictionary,
+        effectively as the reverse of dict2items '''
+
+    if not is_sequence(mylist):
+        raise AnsibleFilterError("items2dict requires a list, got %s instead." % type(mylist))
+
+    return dict((item[key_name], item[value_name]) for item in mylist)
+
+
 def random_mac(value):
     ''' takes string prefix, and return it completed with random bytes
         to get a complete 6 bytes MAC address '''
@@ -653,6 +664,7 @@ class FilterModule(object):
             'extract': extract,
             'flatten': flatten,
             'dict2items': dict_to_list_of_dict_key_value_elements,
+            'items2dict': list_of_dict_key_value_elements_to_dict,
             'subelements': subelements,
 
             # Misc