feat: current_datetime shaper function (#5195)

* current_datetime shaper

* explicitly add current_datetime to the functions allowed in a prompt template

haystack/nodes/other/shaper.py

@@ -1,6 +1,7 @@
 from functools import reduce
 import inspect
 import re
+from datetime import datetime
 from string import Template
 from typing import Literal, Optional, List, Dict, Any, Tuple, Union, Callable
 
@@ -26,6 +27,19 @@ def rename(value: Any) -> Any:
     return value
 
 
+def current_datetime(format: str = "%H:%M:%S %d/%m/%y") -> str:
+    """
+    Function that outputs the current time and/or date formatted according to the parameters.
+
+    Example:
+
+    ```python
+    assert current_datetime("%d.%m.%y %H:%M:%S") == 01.01.2023 12:30:10
+    ```
+    """
+    return datetime.now().strftime(format)
+
+
 def value_to_list(value: Any, target_list: List[Any]) -> List[Any]:
     """
     Transforms a value into a list containing this value as many times as the length of the target list.
@@ -544,6 +558,7 @@ def documents_to_strings(
 
 REGISTERED_FUNCTIONS: Dict[str, Callable[..., Any]] = {
     "rename": rename,
+    "current_datetime": current_datetime,
     "value_to_list": value_to_list,
     "join_lists": join_lists,
     "join_strings": join_strings,

haystack/nodes/prompt/prompt_template.py

@@ -22,6 +22,7 @@ from haystack.nodes.prompt.shapers import (  # pylint: disable=unused-import
     BaseOutputParser,
     AnswerParser,
     to_strings,
+    current_datetime,
     join,  # used as shaping function
     format_document,
     format_answer,
@@ -37,7 +38,10 @@ from haystack.environment import (
 logger = logging.getLogger(__name__)
 
 PROMPT_TEMPLATE_ALLOWED_FUNCTIONS = json.loads(
-    os.environ.get(HAYSTACK_PROMPT_TEMPLATE_ALLOWED_FUNCTIONS, '["join", "to_strings", "replace", "enumerate", "str"]')
+    os.environ.get(
+        HAYSTACK_PROMPT_TEMPLATE_ALLOWED_FUNCTIONS,
+        '["join", "to_strings", "replace", "enumerate", "str", "current_datetime"]',
+    )
 )
 PROMPT_TEMPLATE_SPECIAL_CHAR_ALIAS = {"new_line": "\n", "tab": "\t", "double_quote": '"', "carriage_return": "\r"}
 PROMPT_TEMPLATE_STRIPS = ["'", '"']
@@ -289,7 +293,8 @@ class _FstringParamsTransformer(ast.NodeTransformer):
     def visit_FormattedValue(self, node: ast.FormattedValue) -> Optional[ast.AST]:
         """
         Replaces the f-string expression with a unique ID and stores the corresponding expression in a dictionary.
-        If the expression is the raw `documents` variable, it is encapsulated into a call to `documents_to_strings` to ensure that the documents get rendered correctly.
+        If the expression is the raw `documents` variable, it is encapsulated into a call to `documents_to_strings`
+        to ensure that the documents get rendered correctly.
         """
         super().generic_visit(node)
 

haystack/nodes/prompt/shapers.py

@@ -4,6 +4,7 @@ from haystack.schema import Answer, Document
 
 from haystack.nodes.other.shaper import (  # pylint: disable=unused-import
     Shaper,
+    current_datetime,  # used as shaping function
     join_documents_to_string as join,  # used as shaping function
     format_document,
     format_answer,

test/nodes/test_shaper.py

@@ -1,6 +1,8 @@
-import pytest
+from datetime import datetime
 import logging
 
+import pytest
+
 import haystack
 from haystack import Pipeline, Document, Answer
 from haystack.document_stores.memory import InMemoryDocumentStore
@@ -191,6 +193,46 @@ def test_rename_yaml(tmp_path):
     assert result["invocation_context"]["questions"] == "test query"
 
 
+#
+# current_datetime
+#
+
+
+@pytest.mark.unit
+def test_current_datetime():
+    shaper = Shaper(func="current_datetime", inputs={}, outputs=["date_time"], params={"format": "%y-%m-%d"})
+    results, _ = shaper.run()
+    assert results["invocation_context"]["date_time"] == datetime.now().strftime("%y-%m-%d")
+
+
+@pytest.mark.unit
+def test_current_datetime_yaml(tmp_path):
+    with open(tmp_path / "tmp_config.yml", "w") as tmp_file:
+        tmp_file.write(
+            f"""
+            version: ignore
+            components:
+            - name: shaper
+              type: Shaper
+              params:
+                func: current_datetime
+                params:
+                  format: "%y-%m-%d"
+                outputs:
+                  - date_time
+            pipelines:
+              - name: query
+                nodes:
+                  - name: shaper
+                    inputs:
+                      - Query
+        """
+        )
+    pipeline = Pipeline.load_from_yaml(path=tmp_path / "tmp_config.yml")
+    result = pipeline.run()
+    assert result["invocation_context"]["date_time"] == datetime.now().strftime("%y-%m-%d")
+
+
 #
 # value_to_list
 #