def mergeMultipleBranches(self, collections):
        assert len(collections) > 0

        # Optimize for length 1, which is trivial merge and needs not a
        # lot of work.
        if len(collections) == 1:
            self.replaceBranch(collections[0])
            return

        variable_versions = {}

        for collection in collections:
            for variable, version in iterItems(collection.variable_actives):
                if variable not in variable_versions:
                    variable_versions[variable] = set([version])
                else:
                    variable_versions[variable].add(version)

        for collection in collections:
            for variable, versions in iterItems(variable_versions):
                if variable not in collection.variable_actives:
                    versions.add(0)

        self.variable_actives = {}

        for variable, versions in iterItems(variable_versions):
            if len(versions) == 1:
                version, = versions
            else:
                version = self.addVariableMergeMultipleTrace(
                    variable = variable,
                    traces   = [
                        self.getVariableTrace(variable, version)
                        for version in
                        versions
                    ]
                )

            self.markCurrentVariableTrace(variable, version)
dataset/ETHPy150Open kayhayen/Nuitka/nuitka/optimizations/TraceCollections.py/ConstraintCollectionBase.mergeMultipleBranches/original