Substitution

The d42 package offers capabilities for substituting values in data structures based on defined schemas. This feature is designed to be simple and flexible, allowing for easy handling of complex data substitutions.

Substituting Values

To substitute values, define a schema using d42, and then apply the substitute function with both the schema and the data as arguments.

Here's an example of substituting values in a list of user objects:

from d42 import schema, substitute

UserSchema = schema.dict({
    "id": schema.int,
    "username": schema.str,
})
UserListSchema = schema.list(UserSchema)

substituted = substitute(UserListSchema, [
    {"id": 1, "username": "Bob"},
    {"id": 2, "username": "Alice"}
])

print(substituted)

# schema.list([
#     schema.dict({
#         'id': schema.int(1),
#         'username': schema.str('Bob')
#     }),
#     schema.dict({
#         'id': schema.int(2),
#         'username': schema.str('Alice')
#     })
# ])

This code substitutes values in a user list based on the defined UserListSchema, resulting in a schema.list containing schema.dict elements.

Syntax Sugar

d42 also introduces a more concise syntax for value substitution, using the % operator. This operator is similar to printf-style string formatting in Python, offering a familiar and readable way to substitute values.

Example using the % operator:

from d42 import schema

UserSchema = schema.dict({
    "id": schema.int,
    "username": schema.str,
})
UserListSchema = schema.list(UserSchema)

UserListSchema % [
    {"id": 1, "username": "Bob"},
    {"id": 2, "username": "Alice"}
]

Using the % operator, values are substituted in the user list in a format reminiscent of printf-style string formatting, making the process both intuitive and efficient.