Read SEC submissions in Python with a real response

"""python3 submissions_example.py SNAPSHOT.json; optional live request with SEC_USER_AGENT."""
import json
import os
import re
import sys
from urllib.parse import quote
from urllib.request import Request, urlopen

def filing_rows(payload):
    recent = payload["filings"]["recent"]
    fields = ("accessionNumber", "form", "filingDate", "primaryDocument")
    n = len(recent["accessionNumber"])
    if any(len(recent[name]) != n for name in fields):
        raise ValueError("Unequal SEC column lengths")
    cik = str(int(payload["cik"]))
    for i in range(n):
        row = {name: recent[name][i] for name in fields}
        accession = row["accessionNumber"]
        if not re.fullmatch(r"\d{10}-\d{2}-\d{6}", accession):
            raise ValueError("Invalid accession")
        row["url"] = f"https://www.sec.gov/Archives/edgar/data/{cik}/{accession.replace('-', '')}/{quote(row['primaryDocument'], safe='')}"
        yield row

if __name__ == "__main__":
    if len(sys.argv) > 1:
        with open(sys.argv[1]) as handle:
            payload = json.load(handle)
        mode = "saved SEC response"
    else:
        agent = os.environ["SEC_USER_AGENT"]  # Organization + monitored contact address.
        request = Request("https://data.sec.gov/submissions/CIK0000320193.json", headers={"User-Agent": agent})
        with urlopen(request, timeout=30) as response:
            payload = json.load(response)
        mode = "live SEC response"
    rows = list(filing_rows(payload))
    forms = [r for r in rows if r["form"] in {"10-K", "10-Q", "8-K"}]
    print(json.dumps({"mode": mode, "company": payload["name"], "parsed_rows": len(rows), "selected_examples": forms[:3], "older_history_files": payload["filings"].get("files", []), "limits": "Lists metadata only; linked documents were not fetched or parsed by this example."}, indent=2))