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---
title: Optional keys with defaults (Map/Optional)
---
!!! warning "Experimental"
This feature is in alpha. The API may change on a minor version increment.
Example yaml_snippet:
```yaml
a: 1
```
```python
from strictyaml import Map, Int, Str, Bool, EmptyNone, Optional, load, as_document
from collections import OrderedDict
from ensure import Ensure
schema = Map({"a": Int(), Optional("b", default=False): Bool(), })
```
When parsed the result will include the optional value:
```python
Ensure(load(yaml_snippet, schema).data).equals(OrderedDict([("a", 1), ("b", False)]))
```
If parsed and then output to YAML again the default data won't be there:
```python
print(load(yaml_snippet, schema).as_yaml())
```
```yaml
a: 1
```
When default data is output to YAML it is removed:
```python
print(as_document({"a": 1, "b": False}, schema).as_yaml())
```
```yaml
a: 1
```
When you want a key to stay and default to None:
```python
schema = Map({"a": Int(), Optional("b", default=None, drop_if_none=False): EmptyNone() | Bool(), })
Ensure(load(yaml_snippet, schema).data).equals(OrderedDict([("a", 1), ("b", None)]))
```
!!! note "Executable specification"
Documentation automatically generated from
<a href="https://github.com/crdoconnor/strictyaml/blob/master/hitch/story/optional-with-defaults.story">optional-with-defaults.story
storytests.
|
