QuickFIX Python: tested initiator, acceptor and recovery

Short answer: QuickFIX for Python is the quickfix package on PyPI, a C++ FIX engine with generated Python bindings. Version 1.16.0 (9 May 2026) ships as source only, so pip install quickfix needs a C++17 compiler: on 5 November 2026 it failed on Windows without one and built on Debian 13 with Python 3.12 in about two hours. A local initiator and acceptor then exchanged an order and recovered their sequence numbers after a killed process; order state, duplicates and venue certification remain your job.

QuickFIX's manual is written for C++, with Python covered by short stubs; its examples page names a Python executor in the repository but shows no code. Everything below was run on 5 November 2026 on localhost with synthetic data: no venue, broker or real order. REST against FIX, session rules in general, certification and drop copy are in broker API integration.

Python quickfix install: what happened on 5 November 2026

Expect a long C++ build, because PyPI lists only a 2.8 MB source archive for quickfix 1.16.0 and no wheels.

The Debian build:

FROM python:3.12-slim
RUN apt-get update && apt-get install -y --no-install-recommends g++ make \
 && pip install --no-cache-dir quickfix==1.16.0 simplefix==1.0.17

To keep the result, pip wheel quickfix==1.16.0 -w wheels/ saves a wheel for servers with the same Python and platform (not run here).

QuickFIX Python example: a local initiator and acceptor

Two processes and two config files are enough, because the engine handles logon, heartbeats, sequence numbers and resends.

initiator.cfg:

[DEFAULT]
ConnectionType=initiator
ReconnectInterval=2
FileStorePath=store/initiator
FileLogPath=log/initiator
StartTime=00:00:00
EndTime=00:00:00
UseDataDictionary=Y
DataDictionary=/usr/local/share/quickfix/FIX44.xml

[SESSION]
BeginString=FIX.4.4
SenderCompID=CLIENT
TargetCompID=VENUE
SocketConnectHost=127.0.0.1
SocketConnectPort=5001
HeartBtInt=5

acceptor.cfg uses ConnectionType=acceptor, SocketAcceptPort=5001, the identities swapped, its own paths, and no connect settings or HeartBtInt.

fixapp.py:

import quickfix as fix


class Base(fix.Application):              # SWIG needs all seven callbacks
    def onCreate(self, sid): pass
    def onLogon(self, sid): print("logon", flush=True)
    def onLogout(self, sid): print("logout", flush=True)
    def toAdmin(self, msg, sid): pass
    def fromAdmin(self, msg, sid): pass
    def toApp(self, msg, sid): pass
    def fromApp(self, msg, sid): pass


def run(engine, app, cfg):
    settings = fix.SessionSettings(cfg)
    e = engine(app, fix.FileStoreFactory(settings), settings, fix.FileLogFactory(settings))
    e.start()
    return e

venue.py, a test acceptor that part-fills, then fills the rest after the client disappears:

import threading, time
import quickfix as fix, quickfix44 as fix44
from fixapp import Base, run


class Venue(Base):
    count, order, open = 0, None, False

    def onLogout(self, sid):
        print("logout", flush=True)
        if self.open:
            self.open = False
            threading.Timer(1, self.report, (sid, "F", "2", 100, 60)).start()

    def fromApp(self, msg, sid):
        if msg.getHeader().getField(35) == "D":
            self.order = {t: msg.getField(t) for t in (11, 54, 55)}
            self.open = True
            self.report(sid, "0", "0", 0, 0)
            self.report(sid, "F", "1", 40, 40)

    def report(self, sid, exec_type, status, cum, last):
        self.count += 1
        r = fix44.ExecutionReport()
        for f in (fix.OrderID("V-1"), fix.ExecID(f"E-{self.count}"),
                  fix.ExecType(exec_type), fix.OrdStatus(status),
                  fix.LeavesQty(100 - cum), fix.CumQty(cum), fix.AvgPx(10 if cum else 0),
                  fix.ClOrdID(self.order[11]), fix.Side(self.order[54]),
                  fix.Symbol(self.order[55])):
            r.setField(f)
        if last:
            r.setField(fix.LastQty(last))
            r.setField(fix.LastPx(10))
        ok = fix.Session.sendToTarget(r, sid)
        print("report", exec_type, status, "sendToTarget:", ok, flush=True)


engine = run(fix.SocketAcceptor, Venue(), "acceptor.cfg")   # keep this reference
time.sleep(30)

client.py:

import os, signal, sys, threading, time
import quickfix as fix, quickfix44 as fix44
from fixapp import Base, run

mode = sys.argv[1]
done = threading.Event()


class Client(Base):
    def onLogon(self, sid):
        print("logon", flush=True)
        if mode == "crash":
            o = fix44.NewOrderSingle()
            for f in (fix.ClOrdID("ORD-1"), fix.Symbol("TEST"),
                      fix.Side(fix.Side_BUY), fix.TransactTime(),
                      fix.OrdType(fix.OrdType_LIMIT), fix.OrderQty(100),
                      fix.Price(10)):
                o.setField(f)
            fix.Session.sendToTarget(o, sid)

    def fromApp(self, msg, sid):
        h = msg.getHeader()
        dup = h.isSetField(43) and h.getField(43) == "Y"
        print("seq", h.getField(34), "dup", dup, "exec", msg.getField(17),
              "status", msg.getField(39), "cum", msg.getField(14), flush=True)
        if msg.getField(39) == "1" and mode == "crash":
            os.kill(os.getpid(), signal.SIGKILL)   # no Logout, no state saved
        if msg.getField(39) == "2":
            done.set()


e = run(fix.SocketInitiator, Client(), "initiator.cfg")
done.wait(20)
e.stop()

Run the venue, the client in crash mode, then recover. Client output:

logon
seq 2 dup False exec E-1 status 0 cum 0
seq 3 dup False exec E-2 status 1 cum 40
Killed

logon
seq 3 dup True exec E-2 status 1 cum 40
seq 4 dup True exec E-3 status 2 cum 100
logout

A client started too soon on this loaded machine lost its first Logon in 2 of 5 reruns, and every number moved up by one, so wait for Created session in the acceptor's event log.

Three Python details are missing from the manual. Its Python stub shows default callbacks, but a subclass omitting them died with SWIG director pure virtual method called. Message classes such as fix44.NewOrderSingle() take no fields, unlike the C++ constructors. The engine object must stay referenced: without engine = in venue.py, no logon succeeded in any rerun, and the process usually died with a segmentation fault or abort.

FIX protocol Python example: one session decoded tag by tag

This is the order from that run as logged, with the SOH delimiter shown as |.

8=FIX.4.4|9=115|35=D|34=2|49=CLIENT|52=20261105-14:14:11.386|56=VENUE|11=ORD-1|38=100|40=2|44=10|54=1|55=TEST|60=20261105-14:14:11|10=018|

A separate script recomputed BodyLength and CheckSum for every logged message:

import sys

SOH = "\x01"
bad = n = 0
for line in open(sys.argv[1], encoding="latin-1"):
    raw = line[line.index("8=FIX"):].rstrip("\r\n")
    nine = raw.index(SOH + "9=") + 1
    start = raw.index(SOH, nine) + 1
    end = raw.rindex(SOH + "10=") + 1
    total = sum(raw[:end].encode("latin-1")) % 256
    ok = end - start == int(raw[nine + 2:start - 1]) and raw[end:] == f"10={total:03d}{SOH}"
    n += 1
    bad += not ok
print(n, "messages,", bad, "wrong")

Output: 13 messages, 0 wrong.

Sequence recovery after a dropped link: what the logs show

The engine recovered the gap by itself, but the application received one fill twice.

The client's event log after restart reads:

MsgSeqNum too high, expecting 3 but received 5
Sent ResendRequest FROM: 3 TO: 0
ResendRequest for messages FROM: 3 TO: 4 has been satisfied.

TO: 0 means every later message, as the FIX Session Layer standard (June 2020) defines it. Messages 3 and 4 came back with 43=Y and the original send time in tag 122, and the venue's stored Logon was gap-filled. The process had died inside fromApp, before the engine recorded message 3, so the same fill was delivered again.

Keep processed ExecIDs in storage that survives the process, or take the position from CumQty (tag 14). Order state belongs in an order management system, and the final comparison with the counterparty in position reconciliation.

QuickFIX Python failures, run on localhost

Each row is a test that ran, and sendToTarget returning True with no connection was the most dangerous result.

Python FIX protocol client options: simplefix or QuickFIX

Use simplefix to build and parse messages, and a real engine for sessions, because simplefix has no session layer by design.

simplefix 1.0.17 (12 September 2023, MIT) states on PyPI that it does no socket handling and implements neither FIX recovery nor message persistence. In the test it rebuilt the logged order byte for byte and parsed all 13 logged messages, which suits log tools, test fixtures and simulators.

QuickFIX license, certification and real venues

A passing local test proves engine behavior only, since a real venue adds its own rules, certification and connectivity.

• License. PyPI states none. The archive's LICENSE file is the QuickFIX Software License 1.0, a BSD-style text: keep the notice, include the quickfixengine.org acknowledgment, and do not call derived products QuickFIX.
• Connectivity. This test used plain TCP; the manual's SSL settings were not tested.
• Venue rules. Reset policy, session times, custom tags and certification come from the venue. cTrader's documentation, as one public example and not a recommendation, says it supports FIX 4.4 with no minimum volume or deposit; see cTrader API.
• Conduct. Sending orders you do not intend to trade on a live venue can be market abuse.

Rules depend on your country, and account types and API access vary by firm; no broker is recommended or ranked here. For readers in Turkey, the Capital Markets Board (SPK) said on 23 February 2023 that residents can trade leveraged forex only through institutions it has authorized, and Law No. 6362 provides access blocks for online offers from abroad (Article 99(4)) and criminal penalties for unauthorized activity (Article 109(2)).

Fincode quotes this kind of work through exchange API integration and white-label development, and claims no production FIX work.

Frequently asked questions

Does pip install quickfix work on Windows?

Only with a C++ compiler. On 5 November 2026 it failed on Windows 11 with Python 3.11.3 and no compiler.

Does quickfix work on Python 3.12?

Yes in this test: version 1.16.0 built and ran on Python 3.12.13 on Debian 13 with g++ 14.2.0. PyPI declares Python 3.6 or later; other versions were not tested.

Where is FIX44.xml after pip install?

Under sys.prefix/share/quickfix, which was /usr/local/share/quickfix/FIX44.xml in the test container. Point DataDictionary at that path; a wrong one raised ConfigError.

What does sendToTarget returning True mean?

That the engine accepted and stored the message, which goes out when a connection is established, as the manual's onCreate note says. In the test it returned True with the link down.

Sources

• PyPI: quickfix 1.16.0 (9 May 2026, source distribution only) (opens in a new tab)
• GitHub: quickfix/quickfix README (requirements, build, vcpkg) (opens in a new tab)
• QuickFIX documentation index (C++ with Python and Ruby) (opens in a new tab)
• QuickFIX: Configuration (opens in a new tab)
• QuickFIX: Creating your application (toApp, DoNotSend) (opens in a new tab)
• QuickFIX: Sending messages (opens in a new tab)
• FIX Trading Community: FIX Session Layer Technical Specification (June 2020) (opens in a new tab)
• PyPI: simplefix 1.0.17 (opens in a new tab)
• cTrader Help Center: FIX API (opens in a new tab)
• SPK (Capital Markets Board): Notice on unauthorized leveraged transactions, 23 February 2023 (Turkish) (opens in a new tab)
• Capital Markets Law No. 6362, consolidated text, Articles 99 and 109 (Turkish) (opens in a new tab)

This guide is general information about software and markets, not investment, legal or tax advice. Automated trading can lose money, past or backtested performance does not guarantee future results, and the rules that apply depend on your jurisdiction and your exchange's terms. Sources, checks and corrections: see the editorial policy.