Bug#943786: lmfit-py: failing tests with python3.8

[Steve Langasek]

Source: lmfit-py
Version: 0.9.14-1
Severity: important
User: ubuntu-devel at lists.ubuntu.com
Usertags: origin-ubuntu focal

Dear maintainers,

The lmfit-py package fails to build from source in Ubuntu focal, because
Ubuntu has begun the transition to python3.8 and lmfit-py 0.9.14 is not
source-compatible with python3.8:

[...]
==================================== ERRORS ====================================
_________________ ERROR at setup of test_algebraic_constraints _________________

    @pytest.fixture
    def minimizer():
        """Return the Minimizer object."""
        def residual(pars, x, sigma=None, data=None):
            """Define objective function."""
            yg = gaussian(x, pars['amp_g'], pars['cen_g'], pars['wid_g'])
            yl = lorentzian(x, pars['amp_l'], pars['cen_l'], pars['wid_l'])
    
            model = yg + yl + pars['line_off'] + x * pars['line_slope']
    
            if data is None:
                return model
            if sigma is None:
                return model - data
            return (model-data) / sigma
    
        # generate synthetic data
        n = 601
        xmin = 0.
        xmax = 20.0
        x = np.linspace(xmin, xmax, n)
    
        data = (gaussian(x, 21, 8.1, 1.2) + lorentzian(x, 10, 9.6, 2.4) +
                np.random.normal(scale=0.23, size=n) + x*0.5)
    
        # create initial Parameters
        pars = Parameters()
        pars.add(name='amp_g', value=10)
        pars.add(name='cen_g', value=9)
        pars.add(name='wid_g', value=1)
        pars.add(name='amp_tot', value=20)
        pars.add(name='amp_l', expr='amp_tot - amp_g')
>       pars.add(name='cen_l', expr='1.5+cen_g')

tests/test_algebraic_constraint.py:41: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
lmfit/parameter.py:361: in add
    self.__setitem__(name, Parameter(value=value, name=name, vary=vary,
lmfit/parameter.py:132: in __setitem__
    self._asteval.symtable[key] = par.value
lmfit/parameter.py:823: in value
    return self._getval()
lmfit/parameter.py:805: in _getval
    check_ast_errors(self._expr_eval)
lmfit/parameter.py:25: in check_ast_errors
    expr_eval.raise_exception(None)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <asteval.asteval.Interpreter object at 0x7fe24279e190>, node = None
exc = <class 'NotImplementedError'>, msg = ''
expr = <_ast.Module object at 0x7fe2428fa4f0>, lineno = None

    def raise_exception(self, node, exc=None, msg='', expr=None,
                        lineno=None):
        """Add an exception."""
        if self.error is None:
            self.error = []
        if expr is None:
            expr = self.expr
        if len(self.error) > 0 and not isinstance(node, ast.Module):
            msg = '%s' % msg
        err = ExceptionHolder(node, exc=exc, msg=msg, expr=expr, lineno=lineno)
        self._interrupt = ast.Break()
        self.error.append(err)
        if self.error_msg is None:
            self.error_msg = "%s in expr='%s'" % (msg, self.expr)
        elif len(msg) > 0:
            self.error_msg = "%s\n %s" % (self.error_msg, msg)
        if exc is None:
            try:
                exc = self.error[0].exc
            except:
                exc = RuntimeError
>       raise exc(self.error_msg)
E       NotImplementedError: 'Constant' not supported in expr='<_ast.Module object at 0x7fe2428fa4f0>'

/usr/lib/python3/dist-packages/asteval/asteval.py:248: NotImplementedError
---------------------------- Captured stderr setup -----------------------------
NotImplementedError
   <_ast.Module object at 0x7fe2428fa4f0>
'Constant' not supported
[...]

  (https://launchpad.net/ubuntu/+source/lmfit-py/0.9.14-1/+build/17990659)

Debian has not yet started the transition to python3.8 - the version of
python3-defaults that adds python3.8 as supported is currently in
experimental - but this will eventually become a serious bug in Debian as
well once that transition begins.

For the moment I have worked around the failure in Ubuntu by changing the
packaging to test only against the current version of python3 and not
against all supported versions, but this is a very short-term fix given that
python3.8 will become the default in the next 6 months.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                   https://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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