eblock 0.2.2

A lightweight, async-friendly library for building dynamic, context-aware UI blocks with Pydantic validation and variable substitution.

EBlock (Easy Block Builder)

A flexible, schema-driven library for building dynamic, context-aware content blocks with variable substitution, nested composition, validation, and asynchronous rendering.

Designed for use in page builders, CMS backends, or dynamic UI generation systems where content is defined as structured JSON, rendered with context variables, and validated via Pydantic models.

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Installation

pip install eblock

or with uv:

uv add eblock

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Core Concepts

Context

A container for variables and metadata used during block rendering.

• Variables are case-normalized to uppercase.
• Supports deep copying for safety.
• Allows dynamic assignment via ctx["key"] = value.
• Stores:
  • vars: dictionary of scalar or structured values (strings, numbers, lists, dicts, etc.)
  • extra: arbitrary metadata (not used in substitution)

BaseBlock

Abstract base class for all content blocks.

Each block:

• Accepts properties (dict) on initialization.
• Optionally validates input/output using Pydantic models.
• Recursively resolves {{ variable }} placeholders from Context.
• Supports nesting (blocks inside dicts, lists, etc.).
• Exposes a standardized async build() method.
• Allows custom output transformation via prepare_output().

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Features

✅ Variable substitution
Placeholders like {{ user_name }} are replaced with values from context.

✅ Recursive structure support
Handles dicts, lists, tuples, sets, and nested BaseBlock instances.

✅ Input/Output validation
Define _input_schema and _output_schema using Pydantic models.

✅ Computed fields
Override prepare_output() to add or transform fields after substitution but before output validation.

✅ Static dependency analysis
Use .get_vars() to extract all required variables from a block (including nested ones).

✅ Async-first design
Full async/await support for future extensibility (e.g., async data fetching in prepare_output).

✅ Structured logging
Each block and context instance logs actions with a unique hierarchical logger name.

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Usage Examples

Basic Block

from easy_block_builder import BaseBlock, Context

class TextBlock(BaseBlock):
    _type = "text"

ctx = Context(vars={"name": "Alice"})
block = TextBlock({"content": "Hello, {{ name }}!"})
result, _ = await block.build(ctx)
# result = {"content": "Hello, Alice!"}

Validated Block with Computed Output

from pydantic import BaseModel
from easy_block_builder import BaseBlock

class Input(BaseModel):
    title: str
    score: int

class Output(BaseModel):
    title: str
    score: int
    badge: str

class ScoreCard(BaseBlock):
    _type = "score_card"
    _input_schema = Input
    _output_schema = Output

    async def prepare_output(self, result, ctx):
        result["badge"] = "🏆" if result["score"] >= 90 else "📝"
        return result

Nested Blocks

header = TextBlock({"text": "Welcome, {{ user }}!"})
page = PageBlock({"header": header, "theme": "{{ theme }}"})
# Both `user` and `theme` will be resolved from context

Variable Inspection

block = TextBlock({"msg": "Hi {{ first }}, {{ last }}!"})
print(block.get_vars())  # {"first", "last"}

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API Reference

class Context

• __init__(self, vars: dict | None = None, **extra)
• __getitem__(key), __setitem__(key, value)
• Properties: vars (deep copy), extra (shallow copy)

class BaseBlock

• __init__(self, properties: dict)
• async build(self, ctx: Context) -> tuple[dict, Type[BaseModel] | None]
• async prepare_output(self, result: dict, ctx: Context) -> dict (override to customize)
• get_vars(self) -> set[str]
• Properties: type (read-only)

Class-level attributes (define in subclass)

• _type: str — block identifier (e.g., "image", "form")
• _input_schema: Type[BaseModel] | None
• _output_schema: Type[BaseModel] | None

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Requirements

• Python ≥ 3.10
• Pydantic ≥ 2.0

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Notes

• All string placeholders must use double curly braces: {{ var_name }}.
• Whitespace inside placeholders is stripped: {{ user_id }} → user_id.
• If a variable is missing in context, it resolves to None and logs a warning.
• Blocks are not reusable across different build() calls if they hold mutable state — design them as stateless.