How to Verify US Addresses in Python

What the API returns

Every response is wrapped in a standard envelope. For verification, the Result field is a single object describing the matched address. This is a real response for 1600 Pennsylvania Ave NW:

{
  "Id": "118a23c7-d836-46af-a17f-022a3754e36c",
  "Result": {
    "inputAddress": "1600 Pennsylvania Ave NW Washington DC 20500",
    "fullAddress": "1600 Pennsylvania Ave NW, Washington, DC 20500-0005",
    "addressLine1": "1600 Pennsylvania Ave NW",
    "addressLine2": "Washington, DC 20500-0005",
    "unitType": null,
    "unitNumber": null,
    "city": "Washington",
    "stateCode": "DC",
    "county": "District Of Columbia",
    "zipCode": "20500",
    "zip4": "0005",
    "dpvConfirmation": "Y",
    "deliverableStatus": "Confirmed",
    "confidence": 0.6,
    "matchTier": "Approximate",
    "matchMode": "Speculative",
    "matchCode": {
      "houseNumber": "Matched",
      "street": "Matched",
      "unit": "NotApplicable",
      "city": "Matched",
      "state": "Matched",
      "zipCode": "Matched",
      "zip4": "Inferred"
    },
    "lastVerifiedDate": "2026-06-16T22:40:51",
    "footnotes": ["recovered: standardized via correction, not an exact match"]
  },
  "ClientSessionId": null,
  "StatusCode": 200,
  "IsError": false,
  "Errors": []
}

The fields you'll use most often:

• fullAddress - the postal-standardized address. Store this, not the user's raw input.
• deliverableStatus - a plain-English summary of deliverability (covered below). Branch your checkout on this.
• unitType / unitNumber - the confirmed apartment or suite as discrete fields (e.g. APT, 4B), or null when there is no unit. Only a postal-confirmed unit appears here.
• zip4 and county - appended for you even when the input only had a 5-digit ZIP.
• matchTier and confidence - how the match was reached. The example above is Approximate / 0.6 because speculative mode standardized the input rather than matching it verbatim - still Confirmed as deliverable.
• matchCode - a per-component breakdown (Matched / Corrected / Inferred / Unmatched / NotApplicable) so you can see exactly which fields were trusted versus fixed. (The response also carries postal routing fields - carrierRoute, deliveryPoint, elot - omitted above for brevity.)

Get your API key

1. Sign up at sthan.io and subscribe to the free Address Verification tier
2. Open your dashboard and create an API key
3. Copy the key - it looks like sthan_live_xxxxxxxxxxxxxxxx

You get the key immediately, with no approval queue. An API key is the simplest way to authenticate: you send it as a Bearer token on every request and there is no separate login step. (If you prefer a short-lived token, there is a JWT flow covered later.)

Configure the project

Install requests and keep your key out of source control by reading it from the environment:

pip install requests

# Set the key in your shell (or a .env file loaded by python-dotenv)
export STHAN_API_KEY="sthan_live_xxxxxxxxxxxxxxxx"

import os

STHAN_BASE_URL = "https://api.sthan.io"
STHAN_API_KEY = os.environ["STHAN_API_KEY"]  # raises early if it isn't set

Build the verification client

Use a single requests.Session so the connection pool and the auth header are reused across calls. The client URL-encodes the address, calls the endpoint, unwraps the envelope, and returns the Result object:

import requests
from urllib.parse import quote

# One Session for the whole app: connection pooling + a default auth header
session = requests.Session()
session.headers.update({"Authorization": f"Bearer {STHAN_API_KEY}"})


class VerificationError(Exception):
    """Raised when the API reports a business error in the envelope."""


def verify_address(address: str, mode: str = "speculative",
                   timeout: float = 10.0) -> dict:
    encoded = quote(address.strip(), safe="")
    url = f"{STHAN_BASE_URL}/v2/address-verification/usa/{encoded}"

    response = session.get(url, params={"match": mode}, timeout=timeout)
    response.raise_for_status()  # surfaces 4xx/5xx as an exception

    envelope = response.json()
    if envelope.get("IsError"):
        raise VerificationError(", ".join(envelope.get("Errors", [])))

    return envelope["Result"]

That's the whole integration. One call:

result = verify_address("1600 pennsylvania ave nw washington dc 20500")

print(result["fullAddress"])        # 1600 Pennsylvania Ave NW, Washington, DC 20500-0005
print(result["deliverableStatus"])  # Confirmed
print(result["zip4"])               # 0005

Choose a match mode

The match parameter controls how much typo tolerance the verifier applies. The same call supports four modes, from strictest to loosest:

If you omit match, the endpoint defaults to speculative for the widest recovery. Whichever mode you pick, the location-defining parts of the address - house number, ordinal, directional, state, and the street's core name - are never substituted. A looser mode only widens tolerance for misspellings of the same street, never a jump to a different one.

Interpret the result

deliverableStatus is the one field most integrations branch on. It collapses the raw postal DPV code into four plain values:

For richer logic, pair the status with matchCode. If matchCode["street"] is Corrected, you know the verifier fixed a typo and should show the user the standardized address to confirm. If confidence is below your threshold or matchTier is Speculative, treat the result as a suggestion rather than a fact.

Verify at form submit

Verification belongs on the server, at the moment the user submits - not in the browser. The API does not enable CORS for browser requests, and your API key must never reach client-side JavaScript. Here is a Flask endpoint that verifies the submitted address and returns a decision the front end can act on:

from flask import Flask, request, jsonify

app = Flask(__name__)


@app.post("/checkout/address")
def submit_address():
    raw = (request.json or {}).get("address", "")
    if not raw.strip():
        return jsonify(ok=False, reason="empty"), 400

    try:
        result = verify_address(raw)
    except (requests.RequestException, VerificationError):
        # Don't punish the user for our hiccup: accept, but mark unverified.
        return jsonify(ok=True, verified=False, standardized=raw), 200

    status = result["deliverableStatus"]

    if status == "NotDeliverable":
        return jsonify(
            ok=False,
            reason="not_deliverable",
            message="We couldn't confirm this address is deliverable. "
                    "Please double-check it.",
        ), 422

    warning = None
    if status == "ConfirmedPrimaryOnly":
        warning = "We confirmed the building but not the unit - check the apartment/suite."
    elif status == "Unknown":
        warning = "We couldn't fully confirm this address. Please make sure it's correct."

    return jsonify(
        ok=True,
        verified=(status == "Confirmed"),
        standardized=result["fullAddress"],
        unit={"type": result["unitType"], "number": result["unitNumber"]},
        zip4=result["zip4"],
        warning=warning,
    ), 200

The front end sends the raw address to /checkout/address and gets back a clean, standardized string plus a yes/warn/no decision. Store standardized - the postal-formatted fullAddress - rather than the user's original text, and you've turned a guess into shippable data.

Alternative: JWT authentication

An API key is the simplest option and is all most apps need. If your security policy prefers short-lived credentials, the platform also supports a 2-step JWT flow. You call GET /Auth/Token once with your profileName and profilePassword headers, receive a token valid for up to 60 minutes, then send that token as the Bearer value on subsequent calls:

def get_token() -> str:
    response = session.get(
        f"{STHAN_BASE_URL}/Auth/Token",
        headers={
            "profileName": os.environ["STHAN_PROFILE_NAME"],
            "profilePassword": os.environ["STHAN_PROFILE_PASSWORD"],
        },
        timeout=10,
    )
    response.raise_for_status()
    return response.json()["Result"]["access_token"]


# Swap the static key for a cached token, refreshing on expiry
session.headers.update({"Authorization": f"Bearer {get_token()}"})

Everything else - the endpoint, the envelope, the parsing - stays exactly the same. Cache the token and refresh it shortly before the 60-minute expiry rather than fetching one per request.

Handle errors

Two status codes are worth handling explicitly so a hiccup never blocks a sale:

• 401 - The key or token was rejected. Check the value and, on the JWT flow, refresh and retry once.
• 429 - Rate limit reached. Back off and retry, or accept the address unverified rather than failing the checkout.

import time


def verify_with_retry(address: str, mode: str = "speculative",
                      retries: int = 2) -> dict | None:
    for attempt in range(retries + 1):
        try:
            return verify_address(address, mode)
        except requests.HTTPError as exc:
            if exc.response is not None and exc.response.status_code == 429 \
                    and attempt < retries:
                time.sleep(2 ** attempt)  # 1s, then 2s
                continue
            raise
    return None

The exponential back-off (1s, then 2s) is enough for transient limits. For heavier batch jobs, add a circuit breaker so one bad minute doesn't stall the whole queue.

What's next: fix addresses before they're submitted

Verification confirms an address at submit. You can stop bad addresses even earlier by helping users enter the right one in the first place: Address Autocomplete suggests complete, postal-formatted addresses as the user types, so most submissions are already clean before verification runs. Autocomplete has its own free tier of 100,000 requests/month - pairing the two (autocomplete as they type, one verification call at submit) keeps both your data and your costs in good shape. The Python autocomplete walkthrough is here: Address Autocomplete in Python.

If you need to break an address into components, parse freeform input, or get latitude/longitude, the same envelope and the same requests pattern apply. The full Python walkthrough covering verification, parsing, and geocoding together is in Integrate Address APIs in Python.