Optional Colander Field for object instantiated using custom class

Question

I want to make certain fields in a model made using colander to be optional.
I am familiar with using missing=colander.drop but that only works when SchemaNode is defined.
In case, the field is defined using a custom class, say customeClass = CustomClass(), how to make this as optional?
Below is the snippet:

import colander
class Image(colander.MappingSchema):
    url = colander.SchemaNode(colander.String())
    width = colander.SchemaNode(colander.Int())
    height = colander.SchemaNode(colander.Int())

class Post(colander.MappingSchema):
    id = colander.SchemaNode(colander.Int())
    text = colander.SchemaNode(colander.String())
    score = colander.SchemaNode(colander.Int())
    created_time = colander.SchemaNode(colander.Int())
    attachedImage = Image() # I want to make this as optional

Answer 1

In order to make the custom Class object as optional, we can pass same missing=colander.drop as constructor parameter.

Example:

import colander
class Image(colander.MappingSchema):
    url = colander.SchemaNode(colander.String())
    width = colander.SchemaNode(colander.Int())
    height = colander.SchemaNode(colander.Int())

class Post(colander.MappingSchema):
    id = colander.SchemaNode(colander.Int())
    text = colander.SchemaNode(colander.String())
    score = colander.SchemaNode(colander.Int())
    created_time = colander.SchemaNode(colander.Int())
    attachedImage = Image(missing=colander.drop) # The difference