@ operator lets the assertion rewrite hang up

[Shinkenjoe]

Hi there,

It seems like the @ operator isn't recognized by something int the assertion_rewrite procedure.
With --assert=plain there is no problem.

I did some fake test to single out the problem in fake_matrix.py:

class FakeMatrix:

    def __init__(self, num):
        self.num = num

    def __matmul__(self, other):
        return self.num * other.num

and the test file:

from fake_matrix import FakeMatrix

def test_multmat_operator():
    assert FakeMatrix(2) @ FakeMatrix(3) == 6

traceback:

platform linux -- Python 3.5.0+, pytest-2.8.5, py-1.4.31, pluggy-0.3.1 -- /home/snail/.virtualenvs/fip/bin/python3.5
cachedir: .cache
rootdir: /home/snail/comp/python/fluent/pytest_bug_report, inifile: 
collected 0 items / 1 errors 

================================================================= ERRORS =================================================================
____________________________________________________ ERROR collecting test_multmat.py ____________________________________________________
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/py/_path/local.py:650: in pyimport
    __import__(modname)
<frozen importlib._bootstrap>:969: in _find_and_load
    ???
<frozen importlib._bootstrap>:954: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:892: in _find_spec
    ???
<frozen importlib._bootstrap>:873: in _find_spec_legacy
    ???
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:143: in find_module
    source_stat, co = _rewrite_test(state, fn_pypath)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:290: in _rewrite_test
    rewrite_asserts(tree)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:348: in rewrite_asserts
    AssertionRewriter().run(mod)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:569: in run
    new.extend(self.visit(child))
/usr/lib/python3.5/ast.py:245: in visit
    return visitor(node)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:677: in visit_Assert
    top_condition, explanation = self.visit(assert_.test)
/usr/lib/python3.5/ast.py:245: in visit
    return visitor(node)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:852: in visit_Compare
    left_res, left_expl = self.visit(comp.left)
/usr/lib/python3.5/ast.py:245: in visit
    return visitor(node)
/home/snail/.virtualenvs/fip/lib/python3.5/site-packages/_pytest/assertion/rewrite.py:761: in visit_BinOp
    symbol = binop_map[binop.op.__class__]
E   KeyError: <class '_ast.MatMult'>

My system is debian linux stretch, and as you can see I'm using Python 3.5.0+, pytest-2.8.5 on a virtualenv

[tomviner]

Adding binop_map[ast.MatMult] = "@" did the trick.

See #1361

[tomviner]

Not strictly involved with this bug, but if you over can't sleep, you can look at pytest's generated rewritten ast, converted back to python with these instructions (now updated for Python 3).

For a failing version of your test @Shinkenjoe it generates this:

py.test test_matrix.py -s
============================================================== test session starts ===============================================================
platform linux -- Python 3.5.1, pytest-2.8.8.dev1, py-1.4.31, pluggy-0.3.1
rootdir: /home/tom/Dropbox/DellXPS-backup/dev/pytest-dev/ast_rewrite_gist, inifile: 
collecting 0 items

import builtins as @py_builtins
import _pytest.assertion.rewrite as @pytest_ar
from fake_matrix import FakeMatrix

def test_multmat_operator_non_equal():
    @py_assert1 = 2
    @py_assert3 = FakeMatrix(@py_assert1)
    @py_assert6 = 3
    @py_assert8 = FakeMatrix(@py_assert6)
    @py_assert10 = @py_assert3 @ @py_assert8
    @py_assert12 = 5
    @py_assert11 = @py_assert10 == @py_assert12
    if not @py_assert11:
        @py_format14 = @pytest_ar._call_reprcompare(('==',), (@py_assert11,
            ), (
            """(%(py4)s
{%(py4)s = %(py0)s(%(py2)s)
} @ %(py9)s
{%(py9)s = %(py5)s(%(py7)s)
}) == %(py13)s"""
            ,), (@py_assert10, @py_assert12)) % {'py9': @pytest_ar.
            _saferepr(@py_assert8), 'py13': @pytest_ar._saferepr(
            @py_assert12), 'py2': @pytest_ar._saferepr(@py_assert1), 'py4':
            @pytest_ar._saferepr(@py_assert3), 'py0': @pytest_ar._saferepr(
            FakeMatrix) if 'FakeMatrix' in @py_builtins.locals() or
            @pytest_ar._should_repr_global_name(FakeMatrix) else
            'FakeMatrix', 'py5': @pytest_ar._saferepr(FakeMatrix) if 
            'FakeMatrix' in @py_builtins.locals() or @pytest_ar.
            _should_repr_global_name(FakeMatrix) else 'FakeMatrix', 'py7':
            @pytest_ar._saferepr(@py_assert6)}
        @py_format16 = ('' + 'assert %(py15)s') % {'py15': @py_format14}
        raise AssertionError(@pytest_ar._format_explanation(@py_format16))
    (@py_assert1) = (@py_assert3) = (@py_assert6) = (@py_assert8) = (
        @py_assert10) = (@py_assert11) = (@py_assert12) = None

collected 1 items 

test_matrix.py F

==================================================================== FAILURES ====================================================================
________________________________________________________ test_multmat_operator_non_equal _________________________________________________________

    def test_multmat_operator_non_equal():
>       assert FakeMatrix(2) @ FakeMatrix(3) == 5
E       assert (FakeMatrix(2) @ FakeMatrix(3)) == 5
E        +  where FakeMatrix(2) = FakeMatrix(2)
E        +  and   FakeMatrix(3) = FakeMatrix(3)

test_matrix.py:4: AssertionError
============================================================ 1 failed in 0.01 seconds ============================================================