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NL writer: Add custom exception for no free variables #3445

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NL writer: Add custom exception for no free variables #3445

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a975d4d
add custom exception NLWriterEmptyModelError
alma-walmsley Dec 8, 2024
7fa7521
format with black
alma-walmsley Dec 8, 2024
0e7c7c4
inherit from PyomoException
alma-walmsley Dec 17, 2024
1479ad0
format with black
alma-walmsley Dec 17, 2024
16b601f
remove unused import
alma-walmsley Dec 18, 2024
0b9cdcf
fix tests to assert NLWriterEmptyModelError
alma-walmsley Dec 18, 2024
7815ea6
add `EmptyModelError` to pyomo common errors, add to nl writers
alma-walmsley Dec 31, 2024
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11 changes: 10 additions & 1 deletion pyomo/repn/plugins/nl_writer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,15 @@
)


class NLWriterEmptyModelError(ValueError):
"""
A custom exception to allow handling of a
model with no free variables.
"""

pass
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Suggestion here: We have a "custom" exception from pyomo/common/errors called PyomoException that you might want to inherit from instead. We do this fairly frequently for custom error types so it is also clear when an exception comes from Pyomo as opposed to something else (e.g., gurobipy or idaes).

Example:

from pyomo.common.errors import PyomoException

class MyCustomError(PyomoException):
   """
   My custom error
   """

Also note that you don't need to put pass as long as you have a docstring.

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Fixed, I initially had it inheriting from ValueError since that was raised previously, but I don't suppose there is much need for backwards compatibility in this case!

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Nevermind, there were a couple of tests designed to catch this - I have replaced the asserted exception in those tests



# TODO: make a proper base class
class NLWriterInfo(object):
"""Return type for NLWriter.write()
Expand Down Expand Up @@ -320,7 +329,7 @@ def __call__(self, model, filename, solver_capability, io_options):
if config.symbolic_solver_labels:
os.remove(row_fname)
os.remove(col_fname)
raise ValueError(
raise NLWriterEmptyModelError(
"No variables appear in the Pyomo model constraints or"
" objective. This is not supported by the NL file interface"
)
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