Validating optional keys in mappings (Map)

Not every key in a YAML mapping will be required. If you use the "Optional('key')" validator with YAML, you can signal that a key/value pair is not required.

from strictyaml import Map, Int, Str, Bool, Optional, load
from ensure import Ensure

schema = Map({"a": Int(), Optional("b"): Bool(), })

Valid example 1:

a: 1
b: yes
Ensure(load(yaml_snippet, schema)).equals({"a": 1, "b": True})

Valid example 2:

a: 1
b: no
Ensure(load(yaml_snippet, schema)).equals({"a": 1, "b": False})

Valid example missing key:

a: 1
Ensure(load(yaml_snippet, schema)).equals({"a": 1})

Invalid 1:

a: 1
b: 2
load(yaml_snippet, schema)
when expecting a boolean value (one of "yes", "true", "on", "1", "y", "no", "false", "off", "0", "n")
found an arbitrary integer
  in "<unicode string>", line 2, column 1:
    b: '2'
    ^ (line: 2)

Invalid 2:

a: 1
b: yes
c: 3
load(yaml_snippet, schema)
while parsing a mapping
unexpected key not in schema 'c'
  in "<unicode string>", line 3, column 1:
    c: '3'
    ^ (line: 3)

Executable specification

Documentation automatically generated from optional.story storytests.