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

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Capture and Paste

Use <name> to capture some output and paste it in the next examples.

This quite useful if you have some non-deterministic data that you want to use later:

>>> def gen_number():
...     n = 42
...     print("Generating: %i" % n)
...     return n

>>> a = gen_number()
Generating: <random-number>

>>> a == <random-number>     # byexample: +paste

You can even paste it in the expected of the examples that follows:

>>> a                 # byexample: +paste

>>> a                 # byexample: +paste -capture

Disabling the capture with -tags or -capture you can be sure that the tags come from a previous example and they are not captured from the current example but it is not mandatory.

Pasting works across languages: this is a very convenient way to copy and paste some data from one language to another.

>> puts "This is not very random: <random-number>"  # byexample: +paste
This is not very random: 42


byexample will always try to capture the most smaller string first.

If your named tags are capturing more data than you want, you may want to know what strategies byexample uses.

Using unamed tags <...> or adding more context around the named tag fixes the problem most of the time.

Valid names

Only alphanumeric characters plus the minus and the dot symbols are valid characters for a tag name and a name must starts with a letter or with a dot.

This restricted set prevents unwanted false positives:

>>> def fib():
...     pass

>>> fib
<function fib at <address>>

Disable the tags

With -tags all the tags are taken as literal: the capture tags (<foo>) and the unnamed tags (<...>).

>>> print("hey <a><...><...><a>")   # byexample: -tags
hey <a><...><...><a>

With -capture only the capture tags are taken as literal.

>>> print("hey <a><...> <...><a>")   # byexample: -capture
hey <a><...> <...><a>

New in byexample 10.3.0: the -capture flag was added.


If an example fails, its named tags are not captured.

This may lead to other example fail or abort because the tags that they used cannot be pasted.

This can be a little problematic in the examples that are supposed to do the clean up with -skip.