fix: add deepcopy on the way into MemoryCache

[danielolsen]

Purpose

Addresses #443.

What is the code doing

Add a deepcopy on the way into the cache, so any modifications to the first returned object don't affect the object in the cache.

Testing

>>> from powersimdata import Grid
>>> grid1 = Grid("Texas")
Reading bus.csv
Reading plant.csv
Reading gencost.csv
Reading branch.csv
Reading dcline.csv
Reading sub.csv
Reading bus2sub.csv
Reading zone.csv
>>> grid1.plant.groupby("type").sum().Pmax
type
coal       14501.59
hydro        555.10
ng         68642.42
nuclear     5138.60
solar       2460.20
wind       19062.63
Name: Pmax, dtype: float64
>>> grid1.plant.Pmax = 0
>>> grid1.plant.groupby("type").sum().Pmax
type
coal       0
hydro      0
ng         0
nuclear    0
solar      0
wind       0
Name: Pmax, dtype: int64
>>> grid2 = Grid("Texas")
>>> grid2.plant.groupby("type").sum().Pmax
type
coal       14501.59
hydro        555.10
ng         68642.42
nuclear     5138.60
solar       2460.20
wind       19062.63
Name: Pmax, dtype: float64

Time estimate

30 seconds to understand, more time possibly to discuss.

[BainanXia]

Can we simplify this test to make it easier to read such as:

def test_mem_cache_put_version_never_changes():
    cache = MemoryCache()
    obj = {"key1": "val1"}
    cache.put("foo", obj)
    obj["key2"] = "val2"
    assert "key2" not in cache.get("foo")

[danielolsen]

Sure. I was basically copying and pasting from the test above, but I agree that yours is clearer about what we're trying to do. We could also assert "key1" in cache.get(key).

[jenhagg]

Maybe also assert obj is not cache.get(key)? And possibly assert obj == cache.get(key)

[danielolsen]

I think test_mem_cache_get_returns_copy already catches the first one.

[danielolsen]

Done.

[rouille]

Thanks