# Cwl\_utils Parser Hints vs Requirements
**URL:** https://cwl.discourse.group/t/cwl-utils-parser-hints-vs-requirements/356
**Category:** CWL Questions
**Created:** [May 19, 2021, 8:53pm UTC](https://cwl.discourse.group/t/cwl-utils-parser-hints-vs-requirements/356 "2021-05-19T20:53:28Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@sanaya](https://cwl.discourse.group/u/sanaya)
#### Post date: [May 19, 2021, 8:53pm UTC](https://cwl.discourse.group/t/cwl-utils-parser-hints-vs-requirements/356/1 "2021-05-19T20:53:28Z")
Hello,
I’m working on implementing a CWL parser for the [LANL BEE workflow engine](https://www.lanl.gov/projects/bee/) that uses the `cwl_utils` Python package to parse and verify CWL v1.2 files and I’m having some trouble with CWL hints and requirements.
I noticed that the data structure returned for hints by the CWL v1.2 parser is a list of `ordereddict` objects while for requirements it is a list of distinct objects for each requirement class (e.g. `DockerRequirement` object, `NetworkAccess` object, etc). I was wondering if I could get some insight into why this implementation decision was made so as to guide our own parser design decisions.
Specifically, I was wondering why hints and requirements use different data structures and how this influences the way `cwltool`/`cwl-runner` treats the two in its implementation.
Thanks,
Steven Anaya
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### Author:  [@mrc](https://cwl.discourse.group/u/mrc)
#### Post date: [May 27, 2021, 7:41am UTC](https://cwl.discourse.group/t/cwl-utils-parser-hints-vs-requirements/356/2 "2021-05-27T07:41:29Z")
Welcome @sanaya !
> [@sanaya](#):
>
> I noticed that the data structure returned for hints by the CWL v1.2 parser is a list of `ordereddict` objects while for requirements it is a list of distinct objects for each requirement class (e.g. `DockerRequirement` object, `NetworkAccess` object, etc). I was wondering if I could get some insight into why this implementation decision was made so as to guide our own parser design decisions.
Because `hints` can contain extensions that are not part of the specification, they require extra parsing by the implemenation-agnostic `cwl_utils`
Here is an example of how to do that extra parsing: [https://github.com/common-workflow-language/cwl-utils/blob/8dee31d95177a47c1a85bd7883b0f09e51804c36/cwl\_utils/cite\_extract.py#L35](https://github.com/common-workflow-language/cwl-utils/blob/8dee31d95177a47c1a85bd7883b0f09e51804c36/cwl_utils/cite_extract.py#L35)
We might improve this situation as part of CWL v1.2.1: Implementing [Definition of `hints` is inconsistent · Issue #896 · common-workflow-language/common-workflow-language · GitHub](https://github.com/common-workflow-language/common-workflow-language/issues/896#issuecomment-849406907) would enable `cwl_utils`, `cwljava` and future generated CWL parsers to automatically detect known `hints`
> [@sanaya](#):
>
> Specifically, I was wondering why hints and requirements use different data structures and how this influences the way `cwltool`/`cwl-runner` treats the two in its implementation.
The CWL reference runner `cwltool` does not currently use `cwl_utils` as it predates that package. We hope to someday refactor `cwltool` to build on top of `cwl_utils`.
For `cwltool` the data structures are rather messy and untyped. Once the document is validated to not contain any `requirements` that it doesn’t support then `cwltool` just does lookups for specific extensions, and for the `hints` field it would just ignore any extension hint that it doesn’t know about.
As a reminder: `cwl-runner` is the generic command line name for **any** CWL implementation. If `cwl-runner` is install, then it might point to `cwltool`, `toil-cwl-runner`, `arvados-cwl-runner`, etc…
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### Author:  [@sanaya](https://cwl.discourse.group/u/sanaya)
#### Post date: [May 28, 2021, 9:14pm UTC](https://cwl.discourse.group/t/cwl-utils-parser-hints-vs-requirements/356/3 "2021-05-28T21:14:07Z")
> [@mrc](#):
>
> Because `hints` can contain extensions that are not part of the specification, they require extra parsing by the implemenation-agnostic `cwl_utils`
I didn’t know this about `hints`. Is this so that custom CWL parsers based on `cwl_utils` can implement these extensions specially or are they simply meant to add additional contextual or platform-dependent requirements? What role do `hints` typically have in a real workflow, as opposed to `requirements`?