parsec_api 0.9.0

The official Python library for the Parsec API

Parsec API Python API library

The Parsec API Python library provides convenient access to the Parsec API REST API from any Python 3.9+ application. The library includes type definitions for all request params and response fields, and offers both synchronous and asynchronous clients powered by httpx.

It is generated with Stainless.

Documentation

The REST API documentation can be found on docs.parsecapi.com. The full API of this library can be found in api.md.

Installation

# install from PyPI
pip install parsec_api

Usage

The full API of this library can be found in api.md.

import os
from parsec_api import ParsecAPI

client = ParsecAPI(
    api_key=os.environ.get("PARSEC_API_KEY"),  # This is the default and can be omitted
    # defaults to "production".
    environment="local",
)

markets = client.markets.list(
    exchanges=["kalshi"],
    limit=1,
)
estimate = client.execution_price.retrieve(
    parsec_id=markets.markets[0].parsec_id,
    side="buy",
    amount=10,
)
print(markets.markets)

While you can provide an api_key keyword argument, we recommend using python-dotenv to add PARSEC_API_KEY="My API Key" to your .env file so that your API Key is not stored in source control.

Async usage

Simply import AsyncParsecAPI instead of ParsecAPI and use await with each API call:

import os
import asyncio
from parsec_api import AsyncParsecAPI

client = AsyncParsecAPI(
    api_key=os.environ.get("PARSEC_API_KEY"),  # This is the default and can be omitted
    # defaults to "production".
    environment="local",
)


async def main() -> None:
    markets = await client.markets.list(
        exchanges=["kalshi"],
        limit=1,
    )
    print(markets.markets)


asyncio.run(main())

Functionality between the synchronous and asynchronous clients is otherwise identical.

Examples

The SDK ships with runnable examples in the examples/ directory:

Example	Description
getting_started.py	Fetch markets, read orderbooks, check execution price
order_lifecycle.py	Place, monitor, and cancel an order end-to-end
websocket_streaming.py	Stream real-time orderbook and trade data via WebSocket

Run any example with python examples/getting_started.py (requires PARSEC_API_KEY).

With aiohttp

By default, the async client uses httpx for HTTP requests. However, for improved concurrency performance you may also use aiohttp as the HTTP backend.

You can enable this by installing aiohttp:

# install from PyPI
pip install parsec_api[aiohttp]

Then you can enable it by instantiating the client with http_client=DefaultAioHttpClient():

import os
import asyncio
from parsec_api import DefaultAioHttpClient
from parsec_api import AsyncParsecAPI


async def main() -> None:
    async with AsyncParsecAPI(
        api_key=os.environ.get("PARSEC_API_KEY"),  # This is the default and can be omitted
        http_client=DefaultAioHttpClient(),
    ) as client:
        markets = await client.markets.list(
            exchanges=["kalshi"],
            limit=1,
        )
        print(markets.markets)


asyncio.run(main())

Using types

Nested request parameters are TypedDicts. Responses are Pydantic models which also provide helper methods for things like:

• Serializing back into JSON, model.to_json()
• Converting to a dictionary, model.to_dict()

Typed requests and responses provide autocomplete and documentation within your editor. If you would like to see type errors in VS Code to help catch bugs earlier, set python.analysis.typeCheckingMode to basic.

Nested params

Nested parameters are dictionaries, typed using TypedDict, for example:

from parsec_api import ParsecAPI

client = ParsecAPI()

order = client.orders.create(
    exchange="exchange",
    market_id="market_id",
    outcome="outcome",
    price=0,
    side="buy",
    size=0,
    credentials={},
)
print(order.credentials)

Real-time Streaming

The SDK includes a WebSocket client for streaming orderbook snapshots, deltas, and trade activity in real time. The client maintains a local materialized orderbook, handles authentication, automatic reconnection with exponential backoff, and sequence gap detection.

Important: The ParsecAPI (sync) client's .ws() method returns a ParsecWebSocket, which is async-only. You need asyncio.run() to drive it from synchronous code.

Quick start

from parsec_api import ParsecAPI

client = ParsecAPI(api_key="pk_...")
ws = client.ws()

@ws.on("orderbook")
async def on_book(book):
    print(f"{book.parsec_id} mid={book.mid_price}")

ws.subscribe(parsec_id="polymarket:1234", outcome="yes")

import asyncio
asyncio.run(ws.connect())

Event handlers

Register handlers with the @ws.on(event) decorator and remove them with ws.off(event, fn).

from parsec_api.streaming import OrderbookSnapshot, Activity, WsError

@ws.on("orderbook")
async def handle_book(book: OrderbookSnapshot):
    print(book.bids, book.asks, book.mid_price, book.spread)

@ws.on("activity")
async def handle_activity(activity: Activity):
    print(f"{activity.kind}: {activity.price} x {activity.size}")

@ws.on("error")
async def handle_error(err: WsError):
    print(f"WS error: {err.message}")

@ws.on("disconnected")
async def handle_disconnect(reason: str):
    print(f"Disconnected: {reason}")

@ws.on("reconnecting")
async def handle_reconnect(attempt: int, delay_ms: int):
    print(f"Reconnecting (attempt {attempt}) in {delay_ms}ms")

Available events: orderbook, activity, error, connected, disconnected, reconnecting, heartbeat, slow_reader.

Multiple market subscriptions

You can subscribe to multiple markets at once by passing a list of MarketSubscription objects:

from parsec_api.streaming import MarketSubscription

ws.subscribe([
    MarketSubscription(parsec_id="polymarket:1234", outcome="yes"),
    MarketSubscription(parsec_id="kalshi:KXBTC-25", outcome="yes", depth=10),
])

# Unsubscribe from a single market
ws.unsubscribe(parsec_id="polymarket:1234", outcome="yes")

Connection lifecycle

The client reconnects automatically on disconnect with exponential backoff (up to 30 seconds). Authentication errors are treated as fatal and will not trigger reconnection.

await ws.connect()        # Resolves after successful auth
await ws.close()          # Disconnect, cancel reconnect, clear subscriptions
await ws.run_forever()    # Block until the connection is permanently closed

The client also supports the async context manager protocol:

async with client.ws() as ws:
    ws.subscribe(parsec_id="polymarket:1234", outcome="yes")
    await ws.run_forever()

Accessing the local orderbook

The client maintains a materialized orderbook for each subscription. You can read the current state at any time with get_book():

book = ws.get_book("polymarket:1234", "yes")
if book:
    print(f"Best bid: {book['bids'][0]['price']}, Best ask: {book['asks'][0]['price']}")

Types

Key types are available from parsec_api.streaming:

• ParsecWebSocket — The async WebSocket client
• OrderbookSnapshot — Full orderbook state emitted on every orderbook event
• Activity — Trade or fill event
• WsError — Error payload with optional code and parsec_id
• MarketSubscription — Subscription descriptor (parsec_id, outcome, depth)
• StreamingOrderbookLevel — A single level with price and size fields

Handling errors

When the library is unable to connect to the API (for example, due to network connection problems or a timeout), a subclass of parsec_api.APIConnectionError is raised.

When the API returns a non-success status code (that is, 4xx or 5xx response), a subclass of parsec_api.APIStatusError is raised, containing status_code and response properties.

All errors inherit from parsec_api.APIError.

import parsec_api
from parsec_api import ParsecAPI

client = ParsecAPI()

try:
    client.exchanges.list()
except parsec_api.APIConnectionError as e:
    print("The server could not be reached")
    print(e.__cause__)  # an underlying Exception, likely raised within httpx.
except parsec_api.RateLimitError as e:
    print("A 429 status code was received; we should back off a bit.")
except parsec_api.APIStatusError as e:
    print("Another non-200-range status code was received")
    print(e.status_code)
    print(e.response)
    print(e.code)  # "insufficient_funds" (when provided)
    print(e.retryable)  # True/False (when provided)

Error codes are as follows:

Status Code	Error Type
400	BadRequestError
401	AuthenticationError
403	PermissionDeniedError
404	NotFoundError
422	UnprocessableEntityError
429	RateLimitError
>=500	InternalServerError
N/A	APIConnectionError

Retries

Certain errors are automatically retried 2 times by default, with a short exponential backoff. Connection errors (for example, due to a network connectivity problem), 408 Request Timeout, 409 Conflict, 429 Rate Limit, and >=500 Internal errors are all retried by default.

You can use the max_retries option to configure or disable retry settings:

from parsec_api import ParsecAPI

# Configure the default for all requests:
client = ParsecAPI(
    # default is 2
    max_retries=0,
)

# Or, configure per-request:
client.with_options(max_retries=5).exchanges.list()

Timeouts

By default requests time out after 1 minute. You can configure this with a timeout option, which accepts a float or an httpx.Timeout object:

from parsec_api import ParsecAPI

# Configure the default for all requests:
client = ParsecAPI(
    # 20 seconds (default is 1 minute)
    timeout=20.0,
)

# More granular control:
client = ParsecAPI(
    timeout=httpx.Timeout(60.0, read=5.0, write=10.0, connect=2.0),
)

# Override per-request:
client.with_options(timeout=5.0).exchanges.list()

On timeout, an APITimeoutError is thrown.

Note that requests that time out are retried twice by default.

Advanced

Logging

We use the standard library logging module.

You can enable logging by setting the environment variable PARSEC_API_LOG to info.

$ export PARSEC_API_LOG=info

Or to debug for more verbose logging.

How to tell whether None means null or missing

In an API response, a field may be explicitly null, or missing entirely; in either case, its value is None in this library. You can differentiate the two cases with .model_fields_set:

if response.my_field is None:
  if 'my_field' not in response.model_fields_set:
    print('Got json like {}, without a "my_field" key present at all.')
  else:
    print('Got json like {"my_field": null}.')

Accessing raw response data (e.g. headers)

The "raw" Response object can be accessed by prefixing .with_raw_response. to any HTTP method call, e.g.,

from parsec_api import ParsecAPI

client = ParsecAPI()
response = client.exchanges.with_raw_response.list()
print(response.headers.get('X-My-Header'))

exchange = response.parse()  # get the object that `exchanges.list()` would have returned
print(exchange)

These methods return an APIResponse object.

The async client returns an AsyncAPIResponse with the same structure, the only difference being awaitable methods for reading the response content.

.with_streaming_response

The above interface eagerly reads the full response body when you make the request, which may not always be what you want.

To stream the response body, use .with_streaming_response instead, which requires a context manager and only reads the response body once you call .read(), .text(), .json(), .iter_bytes(), .iter_text(), .iter_lines() or .parse(). In the async client, these are async methods.

with client.exchanges.with_streaming_response.list() as response:
    print(response.headers.get("X-My-Header"))

    for line in response.iter_lines():
        print(line)

The context manager is required so that the response will reliably be closed.

Making custom/undocumented requests

This library is typed for convenient access to the documented API.

If you need to access undocumented endpoints, params, or response properties, the library can still be used.

Undocumented endpoints

To make requests to undocumented endpoints, you can make requests using client.get, client.post, and other http verbs. Options on the client will be respected (such as retries) when making this request.

import httpx

response = client.post(
    "/foo",
    cast_to=httpx.Response,
    body={"my_param": True},
)

print(response.headers.get("x-foo"))

Undocumented request params

If you want to explicitly send an extra param, you can do so with the extra_query, extra_body, and extra_headers request options.

Undocumented response properties

To access undocumented response properties, you can access the extra fields like response.unknown_prop. You can also get all the extra fields on the Pydantic model as a dict with response.model_extra.

Configuring the HTTP client

You can directly override the httpx client to customize it for your use case, including:

• Support for proxies
• Custom transports
• Additional advanced functionality

import httpx
from parsec_api import ParsecAPI, DefaultHttpxClient

client = ParsecAPI(
    # Or use the `PARSEC_API_BASE_URL` env var
    base_url="http://my.test.server.example.com:8083",
    http_client=DefaultHttpxClient(
        proxy="http://my.test.proxy.example.com",
        transport=httpx.HTTPTransport(local_address="0.0.0.0"),
    ),
)

You can also customize the client on a per-request basis by using with_options():

client.with_options(http_client=DefaultHttpxClient(...))

Managing HTTP resources

By default the library closes underlying HTTP connections whenever the client is garbage collected. You can manually close the client using the .close() method if desired, or with a context manager that closes when exiting.

from parsec_api import ParsecAPI

with ParsecAPI() as client:
  # make requests here
  ...

# HTTP client is now closed

Versioning

This package generally follows SemVer conventions, though certain backwards-incompatible changes may be released as minor versions:

1. Changes that only affect static types, without breaking runtime behavior.
2. Changes to library internals which are technically public but not intended or documented for external use. (Please open a GitHub issue to let us know if you are relying on such internals.)
3. Changes that we do not expect to impact the vast majority of users in practice.

We take backwards-compatibility seriously and work hard to ensure you can rely on a smooth upgrade experience.

We are keen for your feedback; please open an issue with questions, bugs, or suggestions.

Determining the installed version

If you've upgraded to the latest version but aren't seeing any new features you were expecting then your python environment is likely still using an older version.

You can determine the version that is being used at runtime with:

import parsec_api
print(parsec_api.__version__)

Requirements

Python 3.9 or higher.

Contributing

See the contributing documentation.