Normalize crashes on discrete variable

[pavlin-policar]

Single Cell version

0.2.4

Orange version

3.10.0.dev0+558d92d

Steps to reproduce the behavior

SingleCellDatasets (Bone marrow AML Markers) -> Normalize

Additional info (worksheets, data, screenshots, ...)

Exception:	AttributeError: 'DiscreteVariable' object has no attribute 'number_of_decimals'
Module:	orangecontrib.single_cell.preprocess.scnormalize:37
Widget Name:	Normalize
Widget Module:	orangecontrib.single_cell.widgets.ownormalization:90
Widget Scheme:	/tmp/ows-j_bzx2sk.ows.xml
Version:	3.10.0.dev0+558d92d
Environment:	Python 3.6.4 on Linux 4.15.2-2-ARCH #1 SMP PREEMPT Thu Feb 8 18:54:52 UTC 2018 x86_64
Installed Packages:	AnyQt==0.0.8, Babel==2.5.1, Bottleneck==1.2.1, CacheControl==0.12.3, CommonMark==0.7.4, Jinja2==2.10, MarkupSafe==1.0, MulticoreTSNE==0.0.1.1, Orange-Spectroscopy==0.3.2, Orange3-DataFusion==0.1.11, Orange3-ImageAnalytics==0.1.15, Orange3-Network==1.3.1, Orange3-Prototypes==0.8.0, Orange3-SingleCell==0.2.4, Orange3==3.10.0.dev0+558d92d, Pillow==5.0.0, PyQt5==5.9.2, Pygments==2.2.0, SecretStorage==2.3.1, Sphinx==1.6.6, alabaster==0.7.10, asn1crypto==0.24.0, astroid==1.6.0, beautifulsoup4==4.6.0, certifi==2017.11.5, cffi==1.11.3, chardet==3.0.4, colorama==0.3.9, colorcet==0.9.1, cryptography==2.1.4, decorator==4.1.2, dill==0.2.7.1, docutils==0.14, flake8-polyfill==1.0.2, flake8==3.5.0, future==0.16.0, h2==2.6.2, h5py==2.7.1, hpack==3.0.0, hyper==0.7.0, hyperframe==3.2.0, idna==2.6, imagesize==0.7.1, ipython-genutils==0.2.0, ipython==6.2.1, isort==4.2.15, jedi==0.11.1, joblib==0.11, jsonschema==2.6.0, jupyter-core==4.4.0, keyring==10.6.0, keyrings.alt==2.3, lap==0.3.0, lazy-object-proxy==1.3.1, lockfile==0.12.2, mando==0.6.4, mccabe==0.6.1, msgpack-python==0.5.1, nbformat==4.4.0, networkx==2.0, numpy==1.14.0, numpydoc==0.7.0, opusFC==1.1.0, pandas==0.22.0, parso==0.1.1, pexpect==4.3.1, pickleshare==0.7.4, pip==9.0.1, plotly==2.2.3, prompt-toolkit==1.0.15, ptyprocess==0.5.2, pycodestyle==2.3.1, pycparser==2.18, pyflakes==1.6.0, pylint==1.8.1, pyqtgraph==0.10.0, python-dateutil==2.6.1, pytz==2017.3, radon==2.2.0, recommonmark==0.4.0, requests==2.18.4, scikit-fusion==0.2.1, scikit-learn==0.19.1, scipy==1.0.0, serverfiles==0.2.1, setuptools==38.4.0, simplegeneric==0.8.1, sip==4.19.6, six==1.11.0, snowballstemmer==1.2.1, spectral==0.19, sphinxcontrib-websupport==1.0.1, traitlets==4.3.2, urllib3==1.22, wcwidth==0.1.7, wheel==0.30.0, wrapt==1.10.11, xlrd==1.1.0
Machine ID:	172461168621546
Stack Trace:	Traceback (most recent call last):  File "/home/pavlin/dev/orange3/Orange/canvas/scheme/widgetsscheme.py", line 832, in process_signals_for_widget    handler(*args)  File "/home/pavlin/dev/orange3-single-cell/orangecontrib/single_cell/widgets/ownormalization.py", line 90, in set_data    self.on_changed()  File "/home/pavlin/dev/orange3-single-cell/orangecontrib/single_cell/widgets/ownormalization.py", line 93, in on_changed    self.commit()  File "/home/pavlin/dev/orange3/Orange/widgets/gui.py", line 2001, in unconditional_commit    do_commit()  File "/home/pavlin/dev/orange3/Orange/widgets/gui.py", line 2009, in do_commit    commit()  File "/home/pavlin/dev/orange3-single-cell/orangecontrib/single_cell/widgets/ownormalization.py", line 112, in commit    data = pp(self.data)  File "/home/pavlin/dev/orange3-single-cell/orangecontrib/single_cell/preprocess/scnormalize.py", line 37, in call    var.number_of_decimals = max(3, var.number_of_decimals)AttributeError: 'DiscreteVariable' object has no attribute 'number_of_decimals'
Local Variables:	OrderedDict([('Y', None),             ('attributes',              [DiscreteVariable(name='cellType', values=['B-cell', 'Megakaryocyte', 'Monocyte', 'NK-cell', 'T-cell'], compute_value=<orangecontrib.single_cell.preprocess.scnormalize.ScShared object at 0x7feca11a3438>)]),             ('data',              [[Monocyte] {ENSG00000163220, S100A9}, [Megakaryocyte] {ENSG00000163736, PPBP}, [Monocyte] {ENSG00000170458, CD14}, [T-cell] {ENSG00000167286, CD3D}, [T-cell] {ENSG00000010610, CD4}, ...]),             ('proj',              <orangecontrib.single_cell.preprocess.scnormalize.ScNormalizeModel object at 0x7feca11a3240>),             ('self', SCNormalizer()),             ('var',              DiscreteVariable(name='cellType', values=['B-cell', 'Megakaryocyte', 'Monocyte', 'NK-cell', 'T-cell'], compute_value=<orangecontrib.single_cell.preprocess.scnormalize.ScShared object at 0x7feca11a3438>))])

[BlazZupan]

@mstrazar can you please take a look?