Add function to parse quantity

[sed-i]

This PR add a utility function for parsing K8s "quantity" from string.
The value is parsed into an absolute (unitless) decimal.Decimal instance, and not into the K8s "canonical representation". This way the code is simpler and values are readily comparable.

References:

1. https://github.com/kubernetes-client/python/blob/master/kubernetes/utils/quantity.py
2. https://github.com/kubernetes/apimachinery/blob/master/pkg/api/resource/quantity.go

Fixes #36.

[gtsystem]

Hi, thanks for your PR. Can you add this function to the documentation together with an example? If you introduce the utils sub-package you can create docs/utils.md

[sed-i]

Thanks @gtsystem! Ready for re-review.

[gtsystem]

I don't see sufficient benefits of supporting dicts. Users can always convert dicts to ResourceRequirements (ResourceRequirements.from_dict). I'll suggest to drop this for now, so that we can have a simpler implementation.

[sed-i]

The dict here is not an alternative representation of
ResourceRequirements, but of ResourceRequirements.limits and ResourceRequirements.requests, i.e. one level down.

The tests demonstrate this. With the overload we're able to do both:

equals_canonically({"cpu": "0.6"}, {"cpu": "600m"})

and

equals_canonically(
    ResourceRequirements(limits={"cpu": "0.6"}), 
    ResourceRequirements(limits={"cpu": "600m"})
)

If feasible, we could change ResourceRequirements to use TypedDict

+class ResourceSpecDict(TypedDict, total=False):
+    cpu: Optional[str]
+    memory: Optional[str]

@dataclass
class ResourceRequirements(DataclassDictMixIn):
-    limits: 'dict' = None
-    requests: 'dict' = None
+    limits: ResourceSpecDict = None
+    requests: ResourceSpecDict = None

In which case the overload would become

@overload
def equals_canonically(first: Optional[ResourceSpecDict], second: Optional[ResourceSpecDict]) -> bool:

[gtsystem]

Got it, I was confused by the function description "Compare two resource requirements for numerical equality." I assumed that the only acceptable type is ResourceRequirements or the equivalent dict. Maybe we can clarify further?

No need to introduce the TypedDict as anyway all the keys are optional and we can have further keys.

[sed-i]

Fixed in next commit.

[gtsystem]

Approved and merged. We have another contribution in progress, once that is completed I will create a public release. Thanks again.