From 84f8b99cf5086c7e7a65450792474e341aeaf209 Mon Sep 17 00:00:00 2001
From: Sadra Barikbin <sadraqazvin1@yahoo.com>
Date: Sun, 27 Jul 2025 01:47:10 +0330
Subject: [PATCH] Apply change

---
 libs/core/langchain_core/prompts/prompt.py    | 13 ++++-----
 .../tests/unit_tests/prompts/test_prompt.py   | 27 +++++++++++++++++++
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/libs/core/langchain_core/prompts/prompt.py b/libs/core/langchain_core/prompts/prompt.py
index 6b77a4e71cb..8c9732b2daf 100644
--- a/libs/core/langchain_core/prompts/prompt.py
+++ b/libs/core/langchain_core/prompts/prompt.py
@@ -137,12 +137,9 @@ class PromptTemplate(StringPromptTemplate):
         """Override the + operator to allow for combining prompt templates."""
         # Allow for easy combining
         if isinstance(other, PromptTemplate):
-            if self.template_format != "f-string":
-                msg = "Adding prompt templates only supported for f-strings."
-                raise ValueError(msg)
-            if other.template_format != "f-string":
-                msg = "Adding prompt templates only supported for f-strings."
-                raise ValueError(msg)
+            if self.template_format != other.template_format:
+                msg = "Cannot add two templates of different formats"
+                raise ValueError(msg) 
             input_variables = list(
                 set(self.input_variables) | set(other.input_variables)
             )
@@ -159,11 +156,11 @@ class PromptTemplate(StringPromptTemplate):
                 template=template,
                 input_variables=input_variables,
                 partial_variables=partial_variables,
-                template_format="f-string",
+                template_format=self.template_format,
                 validate_template=validate_template,
             )
         if isinstance(other, str):
-            prompt = PromptTemplate.from_template(other)
+            prompt = PromptTemplate.from_template(other, template_format=self.template_format)
             return self + prompt
         msg = f"Unsupported operand type for +: {type(other)}"
         raise NotImplementedError(msg)
diff --git a/libs/core/tests/unit_tests/prompts/test_prompt.py b/libs/core/tests/unit_tests/prompts/test_prompt.py
index e092eb66581..12315e1a264 100644
--- a/libs/core/tests/unit_tests/prompts/test_prompt.py
+++ b/libs/core/tests/unit_tests/prompts/test_prompt.py
@@ -681,3 +681,30 @@ def test_prompt_with_template_variable_name_jinja2() -> None:
     template = "This is a {{template}} test."
     prompt = PromptTemplate.from_template(template, template_format="jinja2")
     assert prompt.invoke({"template": "bar"}).to_string() == "This is a bar test."
+
+
+def test_prompt_template_add_with_with_another_format():
+    with pytest.raises(match=r"Cannot add two templates"):
+        PromptTemplate.from_template("This is a {template}") + PromptTemplate.from_template("So {{this}} is", template_format="mustache")
+
+
+@pytest.mark.parametrize(
+        "template_format, prompt1, prompt2",
+        [
+            ("f-string", "This is a {variable}", ". This is {another_variable}"),
+            pytest.param("jinja2", "This is a {{variable}}", ". This is {{another_variable}}", marks=[pytest.mark.requires("jinja2")]),
+            ("mustache", "This is a {{variable}}", ". This is {{another_variable}}"),
+        ]
+)
+def test_prompt_template_add(template_format: str, prompt1: str, prompt2: str) -> None:
+    first_prompt = PromptTemplate.from_template(prompt1, template_format=template_format)
+    second_prompt = PromptTemplate.from_template(prompt2, template_format=template_format)
+
+    concated_prompt = first_prompt + second_prompt
+    prompt_of_concated = PromptTemplate.from_template(prompt1 + prompt2, template_format=template_format)
+
+    assert concated_prompt.input_variables == prompt_of_concated.input_variables
+    assert (
+        concated_prompt.format(variable="template", another_variable="other_template") == 
+        prompt_of_concated.format(variable="template", another_variable="other_template")
+    )
\ No newline at end of file