Lazy, immutable, infinite numeric sequences for Python.
countably lets you describe sequences declaratively, the way you’d write them on paper, and evaluate them on demand:
from countably import count, constant
triangular = count() * (count() + 1) // 2 # 0, 1, 3, 6, 10, ...
powers_of_two = 2 ** count() # 1, 2, 4, 8, 16, ...
every_third = count()[2::3] # 2, 5, 8, 11, ...The primitives are just constant and count. Arithmetic, comparisons, slicing, and element-wise maximum / minimum build everything else. Plain numbers are coerced automatically, so 3 + 5 * count() is equivalent to constant(3) + constant(5) * count().
Highlights
Lazy – elements are computed only on access, with a per-instance 100-item LRU cache for random access. Iteration walks the inputs directly, bypassing the cache.
Immutable – every operation produces a new sequence; nothing is mutated.
Iterable, not iterator – iter(seq) starts fresh every time.
Slices are lazy too – seq[2::3] stays infinite, seq[2:10] is finite with a real len(). Arithmetic between sequences uses the shorter length.
Round / floor / ceil / trunc are supported through the standard Python protocols (math.floor(seq), round(seq)).
Comparisons (<, <=, >, >=) return sequences of booleans, which are numbers in the same world.
See doc/quick-start.rst for usage including a Fibonacci one-liner.
Install
pip install countably1 maintainer
Release files for countably 2026.5.31.3020
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Source distribution (sdist)
| File | Size | Uploaded | |
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| countably-2026.5.31.3020.tar.gz | 13.6 kB | Details |
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|---|---|---|---|---|
| countably-2026.5.31.3020-py3-none-any.whl | Python 3 | none | any | Details |
Total release size: 28.4 kB
Release files / countably-2026.5.31.3020.tar.gz
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