Write snippets of code in your documentation and execute them as regression tests.

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byexample does its best effort to detect common errors and display a solution but not always is easy.

Interpreter not found

byexample uses for most of the languages an external interpreter which must be installed already (byexample will not install it) and be available from the PATH.

In the following example I’m explicitly using an non-existent python interpreter to show you the error:

$ byexample -l python -x-shebang 'python:python2.99' test/    # byexample: +rm= 
[w] Initialization of Python Runner failed.
[!] Something went wrong processing the file 'test/':
The command was not found or was not executable.
The full command line tried is as follows:
This could happen because you do not have it installed or
it is not in the PATH.
Rerun with -vvv to get a full stack trace.

If the interpreter is installed but byexample cannot find it, you can use -x-shebang to put an explicit path.

Something like -x-shebang 'python:/foo/bar/python2.99'. See more about -x-shebang to see the complete syntax.

If you still have troubles, considere opening a ticket.

Prompt not found / Timeout

Every example has a timeout. If byexample does not detect the prompt from the underlying interpreter it will assume that the example hanged.

$ byexample -l python --timeout 1 --ff test/ds/      # byexample: +timeout=15
File "test/ds/", line 7
Failed example:
=> Execution timedout at example 3 of 5.
- This could be because the example just ran too slow (try add more time
with +timeout=<n>) or the example is "syntactically incorrect" and
the interpreter hang (may be you forgot a parenthesis or something like that?).
[FAIL] Pass: 2 Fail: 1 Skip: 2

A timeout can happen because the example is taking too much time or the example is syntactically incorrect.

When an interpreter runs an syntactically incorrect example, it may confuse and wait for more input from the user, input that it will not receive.

Solution? Do a quick check increasing the timeout with +timeout=N. If the problem disappears the example was taking too much time.

If the problem persists, it is probably a syntax error somewhere.

If the error happens in the first example or during the initialization of the interpreter/runner, it may be an incompatibility with byexample. Consider opening a ticket in that case.

Interpreter closed unexpectedly

When you run an example, byexample uses a interpreter or runner for its execution depending of the language that the example was written.

If the example si Python, byexample will use a python interpreter.

The interpreter may close unexpectedly. byexample will detect this and it will abort the execution.

You will see something like this:

$ byexample -l python test/    # byexample: +rm= 
File "test/", line 2
Failed example:
    exit() # I am a bad example ;)
=> Execution of example 1 of 1 crashed.
- Interpreter closed unexpectedly: the interpreter or runner closed unexpectedly.
This could happen because the example triggered a close/shutdown/exit action,
the interpreter was killed by someone else or because the interpreter just crashed.
If the interpreter is just crashing, it may be possible to find a workaround,
you can open an issue at
=> Execution aborted at example 1 of 1.
- Some resources may had not been cleaned.
File test/, 1/1 test ran in <...>
[ABORT] Pass: 0 Fail: 0 Skip: 0

Why an interpreter may close? There are a few possibilities:

  • the example explicitly request the close of the interpreter (like in the example above).
  • the example, somehow, typed ctrl-D (linux) or ctrl-z (windows) which most of the interpreters see this as a close signal.
  • the interpreter was killed by someone else (like someone runs kill -15).
  • if this happens during the initialization of the interpreter, may be it is not supported by byexample.
  • the interpreter just crashed.

What to do? Try to write the smallest example possible that triggers the close. You may find which piece of your example is making the close.

If the interpreter is just crashing or it is failing during the initialization phase, consider opening a ticket. May be it is possible to code a workaround.