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I use pexpect frequently for automating serial-port communications. It’s very useful for implementing test/flashing automation that needs some kind of a serial-port step (such as asking u-boot to run a few commands).

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I do something very similar, how do you deal with random serial port data loss (dropped bytes)? Maybe it is specific to my environment, but I get mangled commands about 1% of time, which really sucks for automated workflows. I mostly countered this by writing commands to a tmp file, verifying md5sum and then executing the file on the device side.

Serial is slow but typically very reliable. If you’re seeing random dropped bytes, I’d take a look at your wiring and PC interface UART which might be low quality. FTDI UARTs in particular are often counterfeit (the real ones are good).

Across a large enough sample set, I definitely see occasional serial errors (although they're rare).

For me, I detect them by checking the exit-code on each command that I run, and also by looking for expected output in response to the commands.

Corrective action is usually a full-stage retry.

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