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'fix_inputs' does not work with empty 'values' dictionary

See original GitHub issue

Description

“Fixing” inputs of a model with an empty values dictionary results in a model that cannot be evaluated due to an undefined variable.

Expected behavior

I would expect mf model to function just like m given that there are no inputs fixed.

Actual behavior

The code crashed due to an undefined variable.

Steps to Reproduce

In [1]: from astropy.modeling import models
   ...: m = models.Identity(2)
   ...: mf = models.fix_inputs(m, {})
   ...: mf(1, 2)
   ...:
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-31-4a2d25efb6e6> in <module>
      2 m = models.Identity(2)
      3 mf = models.fix_inputs(m, {})
----> 4 mf(1, 2)

.../lib/python3.8/site-packages/astropy/modeling/core.py in __call__(self, *args, **kw)
   2818             return outputs
   2819         else:
-> 2820             return self._evaluate(*args, **kw)
   2821
   2822     def _evaluate(self, *args, **kw):

.../lib/python3.8/site-packages/astropy/modeling/core.py in _evaluate(self, *args, **kw)
   2880                 # subindsorted, subvalsorted = list(zip(*subargs))
   2881             # The substitutions must be inserted in order
-> 2882             for ind, val in subargs:
   2883                 newargs.insert(ind, val)
   2884             return self.left(*newargs, **kw)

UnboundLocalError: local variable 'subargs' referenced before assignment

System Details

macOS-10.15.7-x86_64-i386-64bit
Python 3.8.5 (default, Sep  4 2020, 02:22:02)
[Clang 10.0.0 ]
Numpy 1.20.1
astropy 4.2
Scipy 1.6.1
Matplotlib 3.3.4

Issue Analytics

State:
Created 3 years ago
Comments:6 (6 by maintainers)

Top GitHub Comments

1reaction

perrygreenfieldcommented, Mar 1, 2021

I imagine the fix is pretty simple. Test for an empty dictionary and if that is the case, just return the original model.

0reactions

mcaracommented, Mar 1, 2021

Is there a reason why not to fix the code so that subargs is defined and code works on empty dictionaries as well. Of course we can bypass the entire code if we see an empty list but I worry (without understanding the code in depth) that this may be an indication of another problem with the code. What do you think @perrygreenfield ?

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