Blocks

A module for lazy loading Prefect Blocks.

The @lazy_load decorator is centered around a model to attach blocks to. Each block is defined with two parts: a block name and a block property. The block name is a string that identifies the block. The block property is a property that loads the block on first access. The block property should be decorated with the @lazy_load decorator, and the block's type should be specified in the property annotations.

Example:

from prefect.blocks.system import Secret
from prefecto.blocks import lazy_load


class Blocks:
    """Class for lazy loading Prefect Blocks."""

    # Define the block name variables
    password_block: str = "secret-password"

    @property
    @lazy_load("password_block")
    def password(self) -> Secret:
        """The password block."""

blocks = Blocks()
password = blocks.password
print(password)
# Secret(value=SecretStr('**********'))
print(password.get())
# my-secret-password$123

This technique is useful for preventing the blocks from loading until they are actually needed. This can be important during unit testing, where connections to the Prefect server may not exist. The alternative would be to call block.load() directly, which would load the block every time it is called and could lead to performance issues.

The loader can be integrated with pydantic-settings to load block names from environment variables. This can be achieved by setting the block name variables as class variables with default values set to the environment variables.

Example:

from pydantic_settings import BaseSettings, SettingsConfigDict
from prefect.blocks.system import Secret
from prefecto.blocks import lazy_load


class Blocks(BaseSettings):
    """Class for lazy loading Prefect Blocks."""

    model_config = SettingsConfigDict(env_prefix="BLOCKS_")

    # Define the block name variables
    password_block: str = "secret-password"

    @property
    @lazy_load("password_block")
    def password(self) -> Secret:
        """The password block."""

class MyClass:
    block_name = "block_name"

    @property
    @lazy_load("block_name")
    def block(self) -> BlockType:
        """The block."""