[Syed Osama Ali Shah (Osamaali313)]

Problem

_range (in python/semantic_kernel/prompt_template/utils/handlebars_system_helpers.py, backing the {{range}} helper) drops non-integer args by mutating the list while iterating it:

args = list(args)
for index, arg in enumerate(args):
    if not isinstance(arg, int):
        try:
            args[index] = int(arg)
        except ValueError:
            args.pop(index)   # mutating during enumerate()

args.pop(index) shifts the remaining elements left, so the arg immediately after a dropped one is skipped and never validated/converted. That leftover string then reaches range(), raising TypeError.

A single invalid arg works (existing test: {{range 'a' 5}} → [0, 1, 2, 3, 4]), but two consecutive invalid args crash:

{{range 'a' 'b' 5}}  ->  TypeError: 'str' object cannot be interpreted as an integer

which contradicts the helper's drop-invalid-args behavior.

Reproduction (real function)

_range(None, 'a', 5)        -> [0, 1, 2, 3, 4]
_range(None, 'a', 'b', 5)   -> TypeError   (expected [0, 1, 2, 3, 4])

Fix

Build the converted list without mutating during iteration (and tolerate int(None) → TypeError alongside ValueError):

converted = []
for arg in args:
    if isinstance(arg, int):
        converted.append(arg)
    else:
        try:
            converted.append(int(arg))
        except (ValueError, TypeError):
            continue
args = converted

All existing outputs are unchanged.

Test

Adds ("range", "'a' 'b' 5", "[0, 1, 2, 3, 4]") to the parametrized helper test in python/tests/unit/prompt_template/test_handlebars_prompt_template.py — it raises TypeError on the old code and passes after the fix.

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