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Document the memory cost of reading PropertyBitmaps.bitmaps #213

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e9cb49f
Document the memory cost of reading PropertyBitmaps.bitmaps
ulfarsson Nov 6, 2026
8dd1418
Add an example of PropertyBitmaps.bitmaps to its docstring
ulfarsson Nov 6, 2026
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9 changes: 9 additions & 0 deletions permuta/bisc/bisc.py
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Expand Up @@ -511,6 +511,12 @@ class PropertyBitmaps:
permutations, in lexicographic order. `good_counts` maps each length to its
number of good permutations, and `bitmaps` to its bitmap.

`bitmaps` builds the bitmap of a length kept as indices each time it is
asked for it, so `items()`, `values()` and `dict(bitmaps)`, or `bitmaps`
given to another `PropertyBitmaps`, build every such length's bitmap:
10.9 GB for length 14. Asking whether a length is there, iterating over
the lengths and `len()` build none.

Examples:
>>> pb = PropertyBitmaps(Perm.is_increasing)
>>> pb.add_length(3)
Expand All @@ -520,6 +526,9 @@ class PropertyBitmaps:
[Perm((0, 1, 2))]
>>> len(pb.bad[3])
5
>>> pb.add_length(8)
>>> pb.good_counts[8], len(pb.bitmaps[8])
(1, 5040)
"""

def __init__(
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