Deprecating an Algorithm

When the lifetime of an algorithm reaches its limit, it is good practice to signal developers and users of this fact. This signal gives them time to make arrangements for their scripts, either to stop using the algorithm or to use another algorithm. The signal is implemented via “deprecation”.

For the current list of deprecated algorithms, visit the Deprecated category page.

Deprecating a C++ Algorithm

To deprecate an existing C++ algorithm, its associated class must:

  • Inherit from class DeprecatedAlgorithm.

  • Invoke method DeprecatedAlgorithm::deprecatedDate(const std::string &) in the algorithm’s constructor.

  • If another algorithm should be used in place of the deprecated one, invoke method void DeprecatedAlgorithm::useAlgorithm(const std::string &, const int version = -1); in the algorithm’s constructor.

Here are the relevant lines for deprecating algorithm MyOldAlg on Christmas day in 2020 and informing that MyNewAlg should be used

#include "MantidAPI/DeprecatedAlgorithm.h"

class MANTID_ALGORITHMS_DLL MyOldAlg : public API::Algorithm, public API::DeprecatedAlgorithm {
MyOldAlg::MyOldAlg() : m_someMember(0) {

Deprecating a Python Algorithm

To deprecate a Python algorithm, we decorate its associated class with mantid.utils.deprecator.deprecated_algorithm. In the example below we deprecated MyOldAlg on Christmas day in 2020, and inform that MyNewAlg should be used in place of MyOldAlg.

from mantid.utils.deprecator import deprecated_algorithm

@deprecated_algorithm('MyNewAlg', '2020-12-25')
class MyOldAlg(PythonAlgorithm):
    # continued with class definition

If there is no other algorithm to be used in place of MyOlAlg, then an empty string or None must be passed, e.g @deprecated_algorithm(None, '2020-12-25')


Upon using a deprecated algorithm, a message will be printed in the logs at the error level. For instance, when using algorithm MyOldAlg (deprecated on Christmas day in 2020) in place of the new algorithm MyNewAlg, the following error message is printed:

Algorithm "MyOldAlg" is deprecated since 2020-12-25. Use "MyNewAlg" instead

If so desired, the user can raise a RuntimeError by setting property algorithms.deprecated to Raise in the user properties file $HOME/.mantid/, or in a script using ConfigService:

from mantid.kernel import ConfigService
config = ConfigService.Instance()
config['algorithms.deprecated'] = 'Raise'

Coming to our previous example, an error message is printed

Error in execution of algorithm MyOldAlg
Configuration "algorithms.deprecated" set to raise upon use of any deprecated algorithm

To prevent the previous error and instead print a log error message, algorithms.deprecated can be left unset or set to “Log”.


Debug builds set algorithms.deprecated to Raise, the purpose is twofold. First, prevent developers from introducing new source invoking deprecated algorithms. Second, encourage developers to refactor existing source that invokes deprecated algorithms.