[FIX] Only deepcopy the .attributes for the outermost Table transformation

[markotoplak]

Issue

#6189 introduced deep-copying of the dictionary Table.attributes at table transformations. Because table transformations often happen withing table transformation, this can lead to wasting computation and memory. An example of the bug that can happen is Quasars/orange-spectroscopy/pull/726.

For illustration, here is a small example:

import numpy as np
import Orange
from Orange.projection import PCA
from mem_use import MemUse

mem = MemUse()
mem.start()

data = Orange.data.Table(np.random.random((1000, 1000)))
data.attributes["big"] = [ i for i in range(100000) ]
mem.wait_gc("loaded data")

p = PCA(n_components=10)(data)

mem.wait_gc("pca")
mem.draw()

The memory use/time graphs below (first master, then this branch) show big differences (~30 seconds vs 1 second) that all stem from the wasteful use of deepcopy:

Description of changes

The code now only copies .attributes only for the outermost transformations.

And the thing that should be discussed. This PR The previous version of the PR would introduce problems if deeper internal transformations wanted to read table.attributes. I intentionally left it so just to see if there are any problems. I could add support for them by just referencing that dict for non internal transformations, but if any were naughty and actually modified table.attributes, we'd have problems.

I discussed above with myself and noticed that there are no mechanisms for compute_values to set output table.attributes and that even before this PR, if any compute_value was particularly naughty, there were problems. The following test fails on master.

def test_attributes_with_naughty_compute_values(self):
    self.table.attributes["A"] = "Original"
    orig = copy.deepcopy(self.table.attributes)

    def changes_attributes(data: Table):
        self.table.attributes["A"] = "Changed"
        return data.get_column(data.domain.attributes[0])

    ndom = Domain([ContinuousVariable("naughty", compute_value=changes_attributes)])
    new_table = self.table.from_table(ndom, self.table)

    self.assertEqual(orig, new_table.attributes)

The last commit therefore ensures that .attributes are always set, but yes, as before, they should not be modified within the compute_value.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.26%. Comparing base (910d625) to head (4460fbb).
Report is 75 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6849   +/-   ##
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  Coverage   88.26%   88.26%           
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  Files         326      326           
  Lines       71146    71151    +5     
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+ Hits        62796    62801    +5     
  Misses       8350     8350