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ENH: Improve Python errors of mismatched types


This MR addresses and closes #2175 (closed): When using Python API for app.SetParameterValue() with mismatching parameter types, the reported error is cryptic and doesn't help Python-developers to fix the function call. Scientific end-users would be even more troubled by such error messages.


When we pass data of the wrong type or even None to otb.Application.SetParameterValue(), we have no way to know what we did wrong.

In the stack trace we see messages like:

   File "/path/to/OTB-7.2.0-Linux64/lib/python/", line 2920, in SetParameterString
    val = _otbApplication.Application_SetParameterString(self, parameter, value, hasUserValueFlag)
TypeError: in method 'Application_SetParameterString', argument 3 of type 'std::string'

But, which parameter is it? What is its value?

Instead, we could have

  File "/home/luc/dev/tests/OTB-7.2.0-Linux64/lib/python/", line 3239, in SetParameterValue
    raise TypeError('Expected a string for %s, got %s for %s' % (paramKey, type(value), value))
TypeError: Expected a string for elev.geoid, got <class 'NoneType'> for None

Implementation Details

An extra test on the real parameter types has been added for most expected types according to the actual parameters already identified.

Warning: However, this may disable implicit conversions that were previously accepted. We will need to analyse whether things like myapp.SetParameterValue('a_string_parameter', 42) shall be rejected to force the use of myapp.SetParameterValue('a_string_parameter', '42') instead (note the extra quotes around the literal constant number).


No extra test has been written. All preexisting tests shall continue to work.


The copyright owner is CSGroup France and has signed the ORFEO ToolBox Contributor License Agreement.

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Edited by Luc Hermitte

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