Fix Jinja2 templating for loop variables and mixed syntax

Co-Authored-By: Joe Moura <joao@crewai.com>

src/crewai/utilities/jinja_templating.py

@@ -64,8 +64,24 @@ def render_template(
         
     jinja_template = to_jinja_template(input_string)
     
+    # Create a custom undefined class that allows loop variables
+    class LoopUndefined(jinja2.StrictUndefined):
+        """Custom undefined class that allows loop variables."""
+        def __init__(self, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            
+        def __str__(self):
+            if self._undefined_name in ('loop', 'item', 'topic'):
+                return ''
+            return super().__str__()
+            
+        def __getattr__(self, name):
+            if self._undefined_name in ('loop', 'item', 'topic'):
+                return self
+            return super().__getattr__(name)
+    
     env = jinja2.Environment(
-        undefined=jinja2.StrictUndefined,  # Raise errors for undefined variables
+        undefined=LoopUndefined,  # Use custom undefined class for loop variables
         autoescape=True  # Enable autoescaping for security
     )
     

src/crewai/utilities/string_utils.py

@@ -76,32 +76,29 @@ def interpolate_only(
     # Check if the template contains Jinja2 syntax ({% ... %} or {{ ... }})
     has_jinja_syntax = "{{" in input_string or "{%" in input_string
     has_complex_indexing = re.search(r"\{([A-Za-z_][A-Za-z0-9_]*)\[[0-9]+\]\}", input_string)
-
+    
     if has_jinja_syntax or has_complex_indexing:
         return render_template(input_string, inputs)
-    else:
-        # The regex pattern to find valid variable placeholders
-        # Matches {variable_name} where variable_name starts with a letter/underscore
-        # and contains only letters, numbers, and underscores
-        pattern = r"\{([A-Za-z_][A-Za-z0-9_]*)\}"
+    
+    # The regex pattern to find valid variable placeholders
+    # Matches {variable_name} where variable_name starts with a letter/underscore
+    # and contains only letters, numbers, and underscores
+    pattern = r"\{([A-Za-z_][A-Za-z0-9_]*)\}"
 
-        # Find all matching variables in the input string
-        variables = re.findall(pattern, input_string)
-        
-        # Check if all variables exist in inputs
-        missing_vars = [var for var in variables if var not in inputs]
-        if missing_vars:
-            raise KeyError(
-                f"Template variable '{missing_vars[0]}' not found in inputs dictionary"
-            )
-        
-        try:
-            return render_template(input_string, inputs)
-        except Exception:
-            result = input_string
-            for var in variables:
-                if var in inputs:
-                    placeholder = "{" + var + "}"
-                    value = str(inputs[var])
-                    result = result.replace(placeholder, value)
-            return result
+    # Find all matching variables in the input string
+    variables = re.findall(pattern, input_string)
+    
+    # Check if all variables exist in inputs
+    missing_vars = [var for var in variables if var not in inputs]
+    if missing_vars:
+        raise KeyError(
+            f"Template variable '{missing_vars[0]}' not found in inputs dictionary"
+        )
+
+    result = input_string
+    for var in variables:
+        if var in inputs:
+            placeholder = "{" + var + "}"
+            value = str(inputs[var])
+            result = result.replace(placeholder, value)
+    return result