Breakpoints

Pause a lager python script mid-run so you can inspect the bench with ad-hoc lager commands (or a live Python prompt), then resume where it left off. Useful for a long test that reaches a known trouble spot, or for checking on a device in an unknown state without killing and restarting the run. Introduced in lager 0.21.0.

Import

from lager import pause

`pause(label=None, *, timeout=None, interactive=False)`

Blocks the script at the call site until it is resumed (or the timeout elapses).

Argument	Default	Description
`label`	`None`	A short note shown in the pause banner and console — e.g. the reason for the breakpoint.
`timeout`	`None`	Seconds to wait before auto-resuming. `None` uses the `LAGER_BREAKPOINT_TIMEOUT` env var, or 300 s if unset. `0` waits indefinitely (until you resume).
`interactive`	`False`	When `True`, also exposes a Python console attached to the paused script (see Interactive console).

from lager import pause

pause("check the DUT before the final step")

When the line runs, the script prints a banner and stops:

=== lager breakpoint "check the DUT before the final step" at test.py:14  (id 7f3a…e9)
    resume: press Enter here, or `lager python --continue 7f3a…e9 --box mybox`
    inspect: `lager python --console 7f3a…e9 --box mybox`
    auto-resume in 300s

pause() is a safe no-op when it can’t pause — when the script isn’t running under lager python (no breakpoint context), or when breakpoints are disabled. It never raises.

Resuming

A paused script can be resumed three ways:

Press Enter in the terminal running the script (the foreground lager python session).
lager python --continue <id> --box <box> — from any terminal, anywhere. Use the id from the banner. Handy when the script is detached or you’re already in another terminal.
Auto-resume — after the timeout (default 300 s) the script continues on its own and logs that it did. This keeps an unattended or forgotten breakpoint from hanging a run.

Controlling the auto-resume timeout

The default is 300 seconds. Override it per breakpoint, per run, or disable it entirely:

pause("inspect", timeout=1800)   # wait up to 30 minutes
pause("inspect", timeout=0)      # wait forever — never auto-resume

# whole run, via the existing --env flag (applies to pause() calls with no explicit timeout=)
lager python test.py --box mybox --env LAGER_BREAKPOINT_TIMEOUT=1800

Resolution order is timeout= argument → LAGER_BREAKPOINT_TIMEOUT env → 300 s default, so an explicit timeout= in the script wins over the env var.

lager python --timeout is a different setting — the script’s total runtime limit, capped at 300 s on the box — and it will terminate the whole run when it elapses, paused or not. Leave it at its default (0, unlimited) when using long breakpoint pauses.

Interactive console

With pause(interactive=True), the breakpoint also opens a Python console running inside the paused script’s process, seeded with the variables in scope at the pause:

readings = read_adcs()
pause("inspect bench", interactive=True)

Connect to it from another terminal:

lager python --console <id> --box mybox

Connected to interactive console (Ctrl+D to disconnect)
>>> readings
{'adc1': -10.6032, 'adc2': -10.6031, 'adc3': -10.6032}
>>> readings['adc1'] * 1000
-10603.2
>>> read_adcs()
{'adc1': -10.6032, 'adc2': -10.6032, 'adc3': -10.6032}

You can read any variable, evaluate expressions, and call functions the script defines. Ctrl+D disconnects (the script stays paused).

The console is for inspection: it operates on a snapshot of the script’s namespace, so changes you make in the console do not carry back into the running script when it resumes.

Inspecting hardware while paused

Because a paused script holds no box-wide lock, you can run normal lager commands against the bench from another terminal while it waits:

lager supply supply2 state --box mybox     # power supply
lager battery battery1 state --box mybox   # battery
lager adc adc4 --box mybox                 # an ADC the script isn't using

Two hardware rules to keep in mind, both a consequence of USB instruments allowing only one owner at a time:

A device the script itself has open is claimed by the paused process. Reading it from a second terminal returns a “device busy / claimed by another process” error. Read it through the --console instead — that runs in the same process and shares the open handle.
One net per physical instrument per process. Two nets on the same instrument can’t both be open at once in a single script (e.g. the two channels of one Rigol DP821, supply2/supply3, or the dual-role Keithley 2281S, supply1/battery1). Read them from separate terminals, or one at a time.

Built-in `breakpoint()`

Calling Python’s built-in breakpoint() in a lager python script triggers the same interactive pause as lager.pause():

breakpoint()              # same as pause()
breakpoint("check DUT")   # same as pause("check DUT")

Disabling breakpoints

Set LAGER_BREAKPOINTS to an off value to turn every pause() (and breakpoint()) into a no-op — useful for a clean, non-interactive run of a script that has breakpoints left in it:

lager python test.py --box mybox --env LAGER_BREAKPOINTS=off

Accepts off, 0, false, or no (case-insensitive).

Full example

test.py:

import time
from lager import Net, NetType, pause

adc_nets = ["adc1", "adc2", "adc3"]


def read_adcs():
    return {n: round(float(Net.get(n, type=NetType.ADC).input()), 4) for n in adc_nets}


print("Running test...")
for step in range(1, 4):
    print(f"  step {step}/3 ...")
    time.sleep(1)

readings = read_adcs()
print(f"sensor readings: {readings}")

pause("inspect bench before final step", interactive=True)

print("Resuming - running final step.")
print("Done.")

Run it (terminal 1):

lager python test.py --box mybox

Running test...
  step 1/3 ...
  step 2/3 ...
  step 3/3 ...
sensor readings: {'adc1': -10.6032, 'adc2': -10.6031, 'adc3': -10.6032}
=== lager breakpoint "inspect bench before final step" at test.py:18  (id 7f3a…e9)
    resume: press Enter here, or `lager python --continue 7f3a…e9 --box mybox`
    inspect: `lager python --console 7f3a…e9 --box mybox`
    auto-resume in 300s

While it’s paused, check the bench (terminal 2):

lager supply supply2 state --box mybox        # a shared instrument — reads fine
lager python --console 7f3a…e9 --box mybox    # then: readings / read_adcs()

Press Enter in terminal 1 (or run lager python --continue 7f3a…e9 --box mybox) and the script finishes:

=== resumed
Resuming - running final step.
Done.

Getting Started

Development

Power & Simulation

Measurement

I/O & Communication

Utilities

Import

`pause(label=None, *, timeout=None, interactive=False)`

Resuming

Controlling the auto-resume timeout

Interactive console

Inspecting hardware while paused

Built-in `breakpoint()`

Disabling breakpoints

Full example

​Import

​pause(label=None, *, timeout=None, interactive=False)

​Resuming

​Controlling the auto-resume timeout

​Interactive console

​Inspecting hardware while paused

​Built-in breakpoint()

​Disabling breakpoints

​Full example

Import

`pause(label=None, *, timeout=None, interactive=False)`

Resuming

Controlling the auto-resume timeout

Interactive console

Inspecting hardware while paused

Built-in `breakpoint()`

Disabling breakpoints

Full example