pysemantic-layer 0.1.2

Python Open-source semantic layer for Data engineers

PySemantic

A lightweight, graph-based Semantic Layer for Python and SQL.

Define metrics once. Generate SQL everywhere.

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What is PySemantic?

PySemantic lets you define your data models as Python objects -- dimensions, measures, and entity relationships -- and generates correct, optimized SQL from simple metric queries. No more hand-writing joins, no more duplicated business logic scattered across dashboards and notebooks.

from pysemantic.client import SemanticLayer

sl = SemanticLayer(model_path="./models")

sql = sl.query(
    measures=["total_order_price"],
    dimensions=["customer_city"],
    filters=[{"field": "customer_state", "operator": "IN", "value": "('SP', 'RJ')"}],
    order_by=["total_order_price DESC"],
    limit=10,
)

SELECT
  customers.customer_city AS customer_city,
  SUM(order_items.price) AS total_order_price
FROM order_items
LEFT JOIN orders ON order_items.order_id = orders.order_id
LEFT JOIN customers ON orders.customer_id = customers.customer_id
WHERE customers.customer_state IN ('SP', 'RJ')
GROUP BY 1
ORDER BY total_order_price DESC
LIMIT 10

Joins, table references, WHERE vs HAVING -- all resolved automatically from your model definitions.

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Why PySemantic?

	Feature	Description
1	Single source of truth	Define a metric once, use it everywhere
2	Automatic join resolution	Declare entity relationships; PySemantic finds the path
3	SQL injection safe	Structured filters with operator whitelisting and value escaping
4	Dialect support	MySQL, Postgres, and more via SQLGlot
5	Zero infrastructure	Pure Python, no server required at definition time
6	Interactive Studio	Explore your models, graph, and test queries in the browser
7	CLI powered by Typer	Generate SQL and launch the Studio from the terminal

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Installation

pip install pysemantic-layer

Or with Poetry:

poetry add pysemantic-layer

Requires Python 3.11+

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Quick Start

1. Define your models

Create a directory (e.g. models/) with one Python file per table:

# models/orders.py
from pysemantic.modeling import Model, Dimension, Measure, Entity, EntityType

orders = Model(
    name="orders",
    table="orders",
    primary_key="order_id",
    dimensions=[
        Dimension(name="order_status", column="order_status", dtype="string"),
    ],
    measures=[
        Measure(name="total_orders", agg="count", column="order_id"),
        Measure(name="unique_customers", agg="distinct_count", column="customer_id"),
    ],
    entities=[
        Entity(name="order", entity_type=EntityType.PRIMARY, column="order_id"),
        Entity(name="customer", entity_type=EntityType.FOREIGN, column="customer_id"),
    ],
)

# models/customers.py
from pysemantic.modeling import Model, Dimension, Measure, Entity, EntityType

model = Model(
    name="customers",
    table="customers",
    primary_key="customer_id",
    dimensions=[
        Dimension(name="customer_city", column="customer_city", dtype="string"),
        Dimension(name="customer_state", column="customer_state", dtype="string"),
    ],
    measures=[
        Measure(name="total_customers", agg="count", column="customer_id"),
    ],
    entities=[
        Entity(name="customer", entity_type=EntityType.PRIMARY, column="customer_id"),
    ],
)

PySemantic automatically discovers the join path: orders.customer_id (FOREIGN) links to customers.customer_id (PRIMARY) through the shared entity name customer.

2. Query

from pysemantic.client import SemanticLayer

sl = SemanticLayer(model_path="./models")

sql = sl.query(
    measures=["total_orders"],
    dimensions=["customer_city"],
    filters=[{"field": "customer_state", "operator": "=", "value": "SP"}],
    order_by=["total_orders DESC"],
    limit=10,
)
print(sql)

Generated SQL:

SELECT
  customers.customer_city AS customer_city,
  COUNT(orders.order_id) AS total_orders
FROM orders
LEFT JOIN customers
  ON orders.customer_id = customers.customer_id
WHERE
  customers.customer_state = 'SP'
GROUP BY 1
ORDER BY total_orders DESC
LIMIT 10

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PySemantic Studio

PySemantic ships with a built-in interactive web UI powered by Streamlit.

pysemantic studio ./models

The Studio has three tabs:

Tab	What it does
Entity Graph	Interactive visualization of your model relationships. Click nodes to isolate, fullscreen mode, drag & zoom.
Data Dictionary	Browse all registered models with their measures, dimensions, entities, and column mappings.
Query Playground	Pick measures & dimensions from dropdowns, add filters, click "Generate SQL" and see the output. Invalid combos show your error protections in action.

# Custom port and light theme
pysemantic studio ./models --port 8080 --light

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CLI

PySemantic includes a full command-line interface powered by Typer.

pysemantic --help

pysemantic studio -- Launch the web UI

pysemantic studio ./models
pysemantic studio ./models --port 8080 --light

pysemantic query -- Generate SQL from the terminal

# Single measure
pysemantic query ./models -m total_orders -d customer_city --limit 10

# Multiple measures (comma-separated or repeated)
pysemantic query ./models -m "total_orders,unique_customers" -d order_status

# With filters
pysemantic query ./models \
  -m total_order_price \
  -d customer_state \
  -f "customer_state IN ('SP', 'RJ')" \
  -f "total_order_price > 100" \
  --order-by "total_order_price DESC" \
  --limit 5

Filter syntax: "field OPERATOR value" -- supports =, !=, >, <, >=, <=, IN, NOT IN, LIKE, IS, IS NOT.

pysemantic graph -- Export entity graph

pysemantic graph ./models -o my_graph.html

Generates a standalone interactive HTML file with your entity graph.

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Core Concepts

Model

A Model maps to a database table and defines its semantic metadata:

Component	Purpose	Example
Dimensions	Columns to group or filter by	customer_city, order_status
Measures	Aggregated metrics	SUM(price), COUNT(DISTINCT id)
Entities	Relationship keys (PRIMARY / FOREIGN)	order_id, customer_id

Entities & Join Resolution

Entities define how models connect. A PRIMARY entity declares ownership of a concept; a FOREIGN entity references it:

order_items  ──(FK: order)──>  orders  ──(FK: customer)──>  customers
     |
     |──(FK: seller)──>  sellers
     |──(FK: product)──>  products

When you query a measure from order_items with a dimension from customers, PySemantic automatically traverses the graph and generates the required LEFT JOIN chain.

Supported Aggregations

agg value	SQL output
sum	SUM(column)
count	COUNT(column)
avg	AVG(column)
min	MIN(column)
max	MAX(column)
distinct_count	COUNT(DISTINCT column)

Filters

Filters are passed as dictionaries:

{"field": "customer_state", "operator": "IN", "value": "('SP', 'RJ')"}
{"field": "total_order_price", "operator": ">", "value": "1000"}
{"field": "order_status", "operator": "IS", "value": None}

Dimension filters go to WHERE; measure filters go to HAVING -- automatically.

Supported operators: =, !=, >, <, >=, <=, IN, NOT IN, LIKE, ILIKE, IS, IS NOT

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Architecture

User Query (measures, dimensions, filters)
    |
    v
+----------+     +----------+     +----------+
|   AST    |---->| Planner  |---->|Generator |---> SQL string
| (Parser) |     |(Resolver)|     |(Compiler)|
+----------+     +----------+     +----------+
                      |
                +-----+-----+
                | Registry  |
                | + Entity  |
                |   Graph   |
                +-----------+

Layer	Responsibility
AST	Parses raw input into a structured, validated syntax tree
Registry	Loads model files, validates them, builds the entity graph
Planner	Resolves measures/dimensions to models, calculates join paths
Generator	Translates the logical plan into dialect-specific SQL

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API Reference

SemanticLayer

from pysemantic.client import SemanticLayer

sl = SemanticLayer(model_path="./models")

Method	Description
query(measures, dimensions, filters, order_by, limit)	Generate a SQL query string
reload(model_path=None)	Hot-reload models from disk (useful in notebooks)
generate_graph(output_file)	Export an interactive entity graph as HTML

query() Parameters

Parameter	Type	Required	Description
measures	list[str]	Yes	Metric names to aggregate
dimensions	list[str]	No	Dimension names to group by
filters	list[dict]	No	Filter conditions as {field, operator, value} dicts
order_by	list[str]	No	Sort columns (append DESC for descending)
limit	int	No	Maximum rows to return

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License

MIT