From 05304b2f01dbb506804df49e13d93c062f0d4266 Mon Sep 17 00:00:00 2001
From: Jason Dai <jsndai@google.com>
Date: Thu, 20 Mar 2025 18:04:26 -0700
Subject: [PATCH] No public description

PiperOrigin-RevId: 739002065
---
 vertexai/evaluation/prompt_template.py         | 15 ++++++++++-----
 vertexai/preview/evaluation/prompt_template.py | 15 ++++++++++-----
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/vertexai/evaluation/prompt_template.py b/vertexai/evaluation/prompt_template.py
index 473293d20f..256a19d845 100644
--- a/vertexai/evaluation/prompt_template.py
+++ b/vertexai/evaluation/prompt_template.py
@@ -66,11 +66,16 @@ def assemble(self, **kwargs) -> "PromptTemplate":
         Returns:
             A new PromptTemplate instance with the updated template string.
         """
-        replaced_values = {
-            key: kwargs.get(key, "{" + key + "}") for key in self.variables
-        }
-        new_template = self.template.format(**replaced_values)
-        return PromptTemplate(new_template)
+        assembled_string = self.template
+        for variable_name, value in kwargs.items():
+            if variable_name not in self.variables:
+                raise ValueError(
+                    f"Invalid variable name '{variable_name}'. "
+                    f"Valid variables are: {self.variables}"
+                )
+            placeholder = "{" + variable_name + "}"
+            assembled_string = assembled_string.replace(placeholder, str(value))
+        return PromptTemplate(assembled_string)
 
     def __str__(self) -> str:
         """Returns the template string."""
diff --git a/vertexai/preview/evaluation/prompt_template.py b/vertexai/preview/evaluation/prompt_template.py
index 473293d20f..256a19d845 100644
--- a/vertexai/preview/evaluation/prompt_template.py
+++ b/vertexai/preview/evaluation/prompt_template.py
@@ -66,11 +66,16 @@ def assemble(self, **kwargs) -> "PromptTemplate":
         Returns:
             A new PromptTemplate instance with the updated template string.
         """
-        replaced_values = {
-            key: kwargs.get(key, "{" + key + "}") for key in self.variables
-        }
-        new_template = self.template.format(**replaced_values)
-        return PromptTemplate(new_template)
+        assembled_string = self.template
+        for variable_name, value in kwargs.items():
+            if variable_name not in self.variables:
+                raise ValueError(
+                    f"Invalid variable name '{variable_name}'. "
+                    f"Valid variables are: {self.variables}"
+                )
+            placeholder = "{" + variable_name + "}"
+            assembled_string = assembled_string.replace(placeholder, str(value))
+        return PromptTemplate(assembled_string)
 
     def __str__(self) -> str:
         """Returns the template string."""