tn3270lib

Python TN3270/TN3270E client for test automation (IBM-3278 models 2–5). Not an x3270 clone.

Documentation (intended Read the Docs project): https://tn3270lib.readthedocs.io

import tn3270lib
tn = tn3270lib.TN3270(device_type="IBM-3278-3", codepage="cp037")
tn.initiate("host", 23)
tn.wait_for_text("LOGON", timeout=10)
tn.fill("Userid", "IBMUSER")
tn.wait_unlock()
tn.send_enter()
tn.save_screen_html("screen.html")
print(tn.get_screen())
tn.disconnect()

Wait helpers: wait_for_text, wait_unlock, wait_cursor, wait_stable raise TN3270Timeout (screen, cursor, lock, last AID, raw records attached). Field helpers: fields(), field(label) (case-insensitive substring of the preceding protected text), fill, type, tab. Numeric unprotected fields (FA_NUMERIC) reject letters. codepage="cp273" etc.; extra IBM codecs: pip install tn3270lib[i18n]. EW uses the default 24×80 buffer; EWA switches to the model alternate (32×80 / 43×80 / 27×132). SFE/SA store per-cell color and highlighting; save_screen / save_screen_txt / save_screen_html dump the screen (HTML keeps protected vs unprotected and color spans). send_enter / send_pf / send_aid raise TN3270KeyboardLocked while locked and lock again after a successful AID.

TN3270E: BIND_IMAGE is parsed (raw + PLU/SLU/size hints on bind / bind_image); UNBIND clears it. FUNCTIONS advertised are RESPONSES and SYSREQ (not BIND_IMAGE-as-function, not SCS). sysreq() / send_aid('SYSREQ') send a TN3270E REQUEST and toggle SSCP-LU when SYSREQ was negotiated; otherwise the 3270 SYSREQ AID is used. In SSCP-LU mode, type + send_enter send DT_SSCP_LU_DATA (not Read Modified); get_sscp() returns inbound SSCP text. get_nvt() is an ASCII line buffer for DT_NVT and pre-3270 telnet bytes — not a full NVT terminal. Outbound 3270-DATA headers carry an incrementing 16-bit seq (IAC-doubled). Set Reply Mode is honored: field, extended-field (SFE on RM/RB), character (best-effort SA). reconnect() disconnects, resets 3270E/bind/buffers, and initiates again.

TLS defaults to CERT_NONE plus old ciphers for z/OS AT-TLS; verify=True is not the AT-TLS path. Use ssl_context= or certfile= / keyfile= for mTLS. require_tls=True refuses plaintext; allow_plaintext=True restores fallback. STARTTLS, SCS/3287 printer sessions, extra partitions, and DBCS are out of scope. Licensed GPL-3.0-or-later.

Install

From a checkout (the package is not assumed to be on PyPI yet):

pip install .
pip install '.[i18n]'   # extra IBM SBCS codecs
pip install '.[docs]'   # Sphinx / Read the Docs

When published:

pip install tn3270lib
pip install tn3270lib[i18n]

Build artifacts locally (no upload):

python3 -m pip install build twine
python3 -m build
python3 -m twine check dist/*

See CHANGELOG.md for 0.3.0 (parser fixes and phases A–C).