Default values defined in casted types

[lucas-bremond]

Before I submit a PR, would the maintainer be open to allowing the following construct?

ttl = env.timedelta("TTL", default=600)  # Currently works
ttl = env.timedelta("TTL", default=timedelta(minutes=10))  # Raises `environs.EnvValidationError`

The concept could be extended to other types, too: i.e., when the default value is provided in the already casted/output type, then use it as-is.

I think it'd make the interface nicer because expressing durations (for instance) only in seconds is less declarative than using a natural timedelta construct (especially when dealing with more complex durations).

Thoughts?

[fdemmer]

related: #270

[boyleconnor]

This would be especially useful for enums. E.g.:

from environs import Env

env = Env()
env.read_env()

class DataSource(enum.Enum):
    # Possible places from which to mount a data bucket to the inference containers:
    s3 = "s3"
    kubernetes_filesystem = "kubernetes-filesystem"

# This works
DATA_SOURCE: DataSource = env.enum("DATA_SOURCE",DataSource.kubernetes_filesystem.name, type=InferenceDataBucketSource)

# This does not work, but it would if this feature request were implemented
DATA_SOURCE: DataSource = env.enum("DATA_SOURCE",DataSource.kubernetes_filesystem, type=InferenceDataBucketSource)

# Pitfall, do NOT do this:
# This will work when the `name` of an Enum value happens to be the same as its `value`, which is true for _some_, but not all, of the values of this Enum (and many others).
DATA_SOURCE: DataSource = env.enum("DATA_SOURCE",DataSource.kubernetes_filesystem.value, type=InferenceDataBucketSource)

[ddelange]

for timedelta specifically, support for passing a timedelta object as default argument was added in #366

[ddelange]

for future reference leaving this bug here.

float as default is silently downcast to int by marshmallow. float-as-string is correctly rejected by marshmallow (see further below in this test):

https://github.com/sloria/environs/blob/11.2.1/tests/test_environs.py#L235