[Shaurya55555]

Which issue(s) does this change fix?

None filed. I found it while comparing IntrinsicResolver with the newer Fn::Select resolver in cfn_language_extensions.

Why is this change necessary?

CloudFormation accepts the index of Fn::Select as a string. The example in its documentation is { "Fn::Select" : [ "1", [ "apples", "grapes", "oranges", "mangoes" ] ] }, which returns "grapes" (https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-select.html).

IntrinsicResolver.handle_fn_select only accepts an int, so it raises InvalidIntrinsicException for "1". SamBaseProvider.get_template calls the resolver with ignore_errors=True, so the property is silently left unresolved, for example a CodeUri of {"Fn::Select": ["0", {"Fn::Split": [",", {"Ref": "Dirs"}]}]} stays a dict. FnSelectResolver in cfn_language_extensions already accepts a string index, so the two resolvers disagree on the same template.

How does it address the issue?

An index that is a string is converted with int() before the existing type check. A non-numeric string still raises the same error.

Tests: the existing test_fn_select_index_invalid_index_type listed "3" as an invalid index, which encoded the same assumption, so I changed that value to "three". I added test_fn_select_string_index, using the documentation example.

What side effects does this change have?

Templates that pass a quoted index now resolve instead of being left as they are. Integer indexes and all other types behave as before. As in FnSelectResolver, int() also accepts surrounding whitespace and a sign.

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Review the generative AI contribution guidelines (I used an AI assistant, Claude Code, to find and draft this. I reviewed the change and can answer questions about it.)
• Add input/output type hints to new functions/methods (no new functions)
• Write design document if needed (not needed)
• Write/update unit tests
• Write/update integration tests (not needed for this change)
• Write/update functional tests if needed (not needed)
• make pr passes (not run. black --check -l 120 passes on both files, and ruff check shows only a long line in an unrelated existing test that is the same on develop)
• make update-reproducible-reqs if dependencies were changed (no dependencies changed)
• Write documentation (not needed)

How I checked it

The resolver files are copies of develop before and after this change, with a stub for the one unrelated import (get_template_data, used only by Fn::Transform).

• {"Fn::Select": ["1", ["apples", "grapes", "oranges", "mangoes"]]} raises InvalidIntrinsicException before and returns grapes after. "three", None, True, "7" and "-1" still raise.
• resolve_template(ignore_errors=True) on a CodeUri of {"Fn::Select": ["0", {"Fn::Split": [",", {"Ref": "Dirs"}]}]} leaves the dict unresolved before and gives src after (integer index 0 gave src before too).
• The 22 Fn::Select unit tests pass after the change. Running the new test file against the old code, test_fn_select_string_index fails with The argument to Fn::Select must resolve to a int type.
• Not run: the full unit suite, integration tests and make pr.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.