fastmux

Drive and inspect tmux from Python: live session, window, and pane handles with CLI-style reprs

fastmux is a pythonic binding to tmux. tmux() shows every session, window, and pane as a tree, and tmux(target) returns a live Session, Window, or Pane handle, using standard tmux target syntax such as mysess:1.2, %5, or @3. A Pane’s repr is its current screen, its transcript can be indexed and sliced like a list of lines, any scope can be searched rg-style, and panes are driven with send, send_keys, and friends. fastmux.bg adds named, managed background sessions on top: create-or-reuse a session by name and drive it by sid, so an agent and a user can share the same terminal.

Install

pip install fastmux

You will also need tmux itself installed and on your PATH.

Getting started

import sys
from fastmux import *

Start a throwaway session running anything you like. It’s created detached, so your terminal is untouched:

s = new_session([sys.executable,'-u','-c','import time\n'
                                          'for i in range(30): print(f"line {i}")\n'
                                          'time.sleep(600)'],
                width=60, height=8)
p = s.pane
p.poll(wait_ms=2000)  # wait for output to arrive
p

line 23
line 24
line 25
line 26
line 27
line 28
line 29

A Pane’s repr is its live screen. The whole transcript (scrollback included) works like a list of lines:

len(p), p[0], p[-1], p[5:7].lines

(30, 'line 0', 'line 29', ('line 5', 'line 6'))

Split panes with the directional verbs rsplit, bsplit, lsplit, and asplit (no tmux -h/-v confusion), again without stealing focus:

p.bsplit(size=3, cmd="top")
s.windows

1: nbs* (2 panes) @0
  1.1: [60x4] %0 python (active)
  1.2: [60x3] %1 tmux

Panes can also be driven directly: p.send('ls\n') pastes text and polls for the response, p.send_keys('C-c') sends tmux key names, and p.wait() returns an exit status. See the full docs for the complete API.

Search any scope (one pane, a window, a session, or every terminal you have) and get rg-style hits whose target can be pasted straight back into tmux():

hits = s.search('line 2')
hits

0:1.1:2: line 2
0:1.1:20: line 20
0:1.1:21: line 21
0:1.1:22: line 22
0:1.1:23: line 23
0:1.1:24: line 24
0:1.1:25: line 25
0:1.1:26: line 26
0:1.1:27: line 27
0:1.1:28: line 28
0:1.1:29: line 29

tmux(hits[0].target)[-3:]

line 27
line 28
line 29
── 0:1.1 %0 · lines 27-30 of 30

And tmux() alone shows everything as a tree of sessions, windows, and panes:

tmux()

0: 1 windows
  1: nbs* (2 panes) @0
    1.1: [60x4] %0 python (active)
    1.2: [60x3] %1 top

s.kill()

Background sessions

A handle like p only helps while you can hold it. A background session outlives that: it is created in one tool call, driven from another, and shared with a user who attaches by name. fastmux.bg addresses sessions by sid — a session name, a %pane_id, a handle, or None for the current pane — and start_session creates-or-reuses, so the same line works in every call:

from fastmux.bg import *

sid = 'fastmux-demo-bg'
start_session(sid, width=60, height=8)
send(sid, 'echo $((6*7)) apples\n', wait_ms=2000)

The user can watch or type alongside with tmux attach -t fastmux-demo-bg, and polling is seen-state based: output that arrived while nobody was watching satisfies the next poll(sid) immediately, rather than making it wait for yet another change. managed_sessions() lists every session start_session created, and close(sid) kills one:

managed_sessions()

close(sid)