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update assert docs

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Benjamin Peterson 2011-06-29 10:52:39 -05:00
parent aa7f7a1c71
commit 4fcd346838
1 changed files with 12 additions and 12 deletions
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doc/assert.txt
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@ -196,30 +196,32 @@ Reporting details about a failing assertion is achieved either by rewriting
assert statements before they are run or re-evaluating the assert expression and assert statements before they are run or re-evaluating the assert expression and
recording the intermediate values. Which technique is used depends on the recording the intermediate values. Which technique is used depends on the
location of the assert, py.test's configuration, and Python version being used location of the assert, py.test's configuration, and Python version being used
to run py.test. However, for assert statements with a manually provided to run py.test. Note that for assert statements with a manually provided
message, i.e. ``assert expr, message``, no assertion introspection takes place and the manually provided message will be rendered in tracebacks. message, i.e. ``assert expr, message``, no assertion introspection takes place
and the manually provided message will be rendered in tracebacks.
By default, if the Python version is greater than or equal to 2.6, py.test By default, if the Python version is greater than or equal to 2.6, py.test
rewrites assert statements in test modules. Rewritten assert statements put rewrites assert statements in test modules. Rewritten assert statements put
introspection information into the assertion failure message. py.test only introspection information into the assertion failure message. py.test only
rewrites test modules directly discovered by its test collection process, so rewrites test modules directly discovered by its test collection process, so
asserts in supporting modules will not be rewritten. asserts in supporting modules which are not themselves test modules will not be
rewritten.
.. note:: .. note::
py.test rewrites test modules as it collects tests from them. It does this by py.test rewrites test modules on import. It does this by using an import hook
writing a new pyc file which Python loads when the test module is to write a new pyc files. Most of the time this works transparently. However,
imported. If the module has already been loaded (it is in sys.modules), if you are messing with import yourself, the import hook may interfere. If
though, Python will not load the rewritten module. This means if a test this is the case, simply use ``--assertmode=reinterp`` or
module imports another test module which has not already been rewritten, then ``--assertmode=off``. Additionally, rewriting will fail silently if it cannot
py.test will not be able to rewrite the second module. write new pycs, i.e. in a read-only filesystem or a zipfile.
If an assert statement has not been rewritten or the Python version is less than If an assert statement has not been rewritten or the Python version is less than
2.6, py.test falls back on assert reinterpretation. In assert reinterpretation, 2.6, py.test falls back on assert reinterpretation. In assert reinterpretation,
py.test walks the frame of the function containing the assert statement to py.test walks the frame of the function containing the assert statement to
discover sub-expression results of the failing assert statement. You can force discover sub-expression results of the failing assert statement. You can force
py.test to always use assertion reinterpretation by passing the py.test to always use assertion reinterpretation by passing the
``--assertmode=old`` option. ``--assertmode=reinterp`` option.
Assert reinterpretation has a caveat not present with assert rewriting: If Assert reinterpretation has a caveat not present with assert rewriting: If
evaluating the assert expression has side effects you may get a warning that the evaluating the assert expression has side effects you may get a warning that the
@ -244,5 +246,3 @@ All assert introspection can be turned off by passing ``--assertmode=off``.
.. versionchanged:: 2.1 .. versionchanged:: 2.1
Introduce the ``--assertmode`` option. Deprecate ``--no-assert`` and Introduce the ``--assertmode`` option. Deprecate ``--no-assert`` and
``--nomagic``. ``--nomagic``.