Missing keys, None, and defaults

Missing and None are different inputs

Optional(str) permits an absent key, which is omitted from the result. str | None accepts a present null value but still requires the key. Optional(str, 'Ada') inserts a default only when the key is absent.

from zodify import Optional, validate

print(validate({"name": Optional(str)}, {}))
print(validate({"name": str | None}, {"name": None}))
print(validate({"name": Optional(str, "Ada")}, {}))

# Defaults are trusted: neither copied nor validated.
default = []
result = validate({"items": Optional([str], default)}, {})
print("Shares default:", result["items"] is default)
print(validate({"count": Optional(int, "unchecked")}, {}))

try:
    validate({"name": str | None}, {})
except ValueError as error:
    print(f"ValueError: {error}")

{}
{'name': None}
{'name': 'Ada'}
Shares default: True
{'count': 'unchecked'}
ValueError: name: missing required key

Defaults in the released version

In 0.8.1, a default is inserted as supplied. It is not independently validated or copied. Mutable defaults may be shared between calls. The example shows how an incorrectly typed default is still inserted. Use type-correct defaults in application code.

Prefer immutable, type-correct defaults and construct fresh mutable values in application code. Check the compatibility notes for the installed release before changing a default policy.

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