Stabilize Python pynput keystroke loops on macOS: release Enter to prevent skipped delays

Learn why Python pynput loops skip delays in macOS Messages and how to fix timing: pair Enter press with release. Stabilize keystroke automation. Avoid misfire.

Automating keystrokes with Python often looks straightforward until subtle details of input emulation collide with timing. A common pattern is to type text, pause, and hit Enter in a loop. It may behave correctly on the first pass and then deteriorate: delays seem to be ignored between typing and sending, and some messages go out before typing completes. Here is a practical example of that pitfall and a minimal fix that makes the loop stable.

Reproducible scenario

The following script opens the Messages app on macOS, waits for the UI to be ready, types a message, pauses, presses Enter, and repeats. The issue shows up after the first iteration: the delay between type and press intermittently appears to be skipped, and Enter fires too early.

import os as ops
import time as tm
from pynput.keyboard import Key as K, Controller as KbCtl

ops.system("open -a Messages")

tm.sleep(3)

kb = KbCtl()

for idx in range(50):
    kb.type("Example Message")
    print("Message typed")
    tm.sleep(5)
    kb.press(K.enter)
    print(f"======= {idx+1} Message(s) Sent =======")
    tm.sleep(40)

print("Texting Complete")

What’s actually happening

The crux is in how key events are emitted. Calling press keeps the key in a pressed state. Without a corresponding release, that state persists across iterations. Because pynput runs its event dispatching in a separate thread, time.sleep in the main thread does not block that background activity. As a result, Enter can remain logically pressed while the loop sleeps and resumes, which explains why messages can be submitted before typing finishes. The print calls continue to respect the configured pauses because they run in the main thread where the sleep happens.

Fix: balance press with release

The stable approach is to release the key after pressing it. This clears the pressed state before the next iteration starts, eliminating the premature submission of partially typed messages.

import os as ops
import time as tm
from pynput.keyboard import Key as K, Controller as KbCtl

ops.system("open -a Messages")

tm.sleep(3)

kb = KbCtl()

for idx in range(50):
    kb.type("Example Message")
    print("Message typed")
    tm.sleep(5)
    kb.press(K.enter)
    kb.release(K.enter)
    print(f"======= {idx+1} Message(s) Sent =======")
    tm.sleep(40)

print("Texting Complete")

Why this matters

In input automation, the difference between a momentary tap and a sustained press is critical. When a key remains held, subsequent operations can be affected in ways that look like timing drift or ignored sleeps, even though the delays are honored by the main thread. Understanding that the input emitter works concurrently helps reason about these symptoms and prevents flaky behavior—especially in loops that control UI actions like submitting a message.

Takeaways

If your loop types text and then sends it, ensure that any press is paired with a release. Changing runtimes or launching methods won’t resolve a stuck key state; balancing key events will. Keep the pauses where you need them for UI readiness, and treat press/release as a single, intentional keystroke to avoid sporadic early submissions.