clj

clj is a collection of functions to work with lazy iterators in Python.

It’s a module for those times when you did too much Clojure and came back to Python wondering where are all these distinct, drop-while, cycle, first, etc.

The library is oriented toward laziness and performance. Functions are implemented with as little overhead as possible.

Install

pip install clj

Python requirement:

• 0.4.x: Python 3.9+
• 0.3.x: Python 3.7+
• 0.2.x: Python 3.7+
• 0.1.x: Python 2.7, 3.3+

Usage

The library is considered stable and is used in production.

Example

;; Clojure
(->> coll (map inc) (filter even?) distinct count println)
; which expands to:
(println (count (distinct (filter even? (map inc coll)))))

# Python
from clj import count, distinct, inc, is_even

print(count(distinct(filter(is_even, map(inc, coll)))))

Note that count() works on both sequences in generators; in the latter case it doesn’t load everything in memory like e.g. len(list(g)) would do.

Core Ideas

• Lazy by default. All functions should work on arbitrary iterators and return generators.
• This is Python. We keep Python’s semantics instead of trying to reproduce Clojure in Python (e.g. 0 and [] are logically true in Clojure but false in Python; None is not equivalent to an empty collection).
• Don’t Reinvent the Wheel. We don’t reimplement built-in functions unless they miss something, like range that can’t be called without argument to yield an infinite sequence.

Support

The general naming scheme is: use underscores instead of hyphens; start the function with is_ if its Clojure counterparts ends with a ?.

Sequences

We aim to implement all Clojure functions that operate on sequences (see the list here). They all work on iterables and return generators by default (Python’s closest equivalent of lazy seqs). We don’t support transducers.

Clojure	clj	Comment
distinct	distinct
filter	filter	Alias to Python’s built-in filter.
remove	remove
keep	keep
keep-indexed	keep_indexed
cons	cons
concat	concat	Equivalent to itertools.chain.
lazy-cat	-	Use Python’s itertools.chain.
mapcat	mapcat
cycle	cycle
interleave	interleave
interpose	interpose
rest	rest
next	-	Use rest.
fnext	-	Use second.
nnext	-	Use rest(rest(…))
drop	drop
drop-while	drop_while	Equivalent to itertools.dropwhile.
nthnext	-	Use drop.
take	take
take-nth	take_nth
take-while	take_while	Equivalent to itertools.takewhile.
butlast	butlast
drop-last	drop_last
flatten	flatten
reverse	reverse
sort	-	Use Python’s built-in sort.
sort-by	-	Use sort(…, key=your_function).
shuffle	shuffle
split-at	split_at
split-with	split_with
partition	partition	(partition n step pad coll) becomes partition(coll, n, step, pad). Only the case step=n is supported for now.
partition-all
partition-by	partition_by
map	map	Alias to Python’s built-in map.
pmap	-
replace	replace
reductions	reductions	(reductions f i c) becomes reductions(f, c, i).
map-indexed	map_indexed
seque	-
first	first	None is not a valid parameter.
ffirst	ffirst	None is not a valid parameter.
nfirst	nfirst
second	second
nth	nth
last	last
rand-nth	-	Use Python’s random.choice.
zipmap	zipmap
into	-
reduce	-	Use Python’s functools.reduce.
set	-	Use Python’s set.
vec	-	Use Python’s list.
into-array	-	Use Python’s list.
to-array-2d	-
frequencies	-	Use Python’s collections.Counter.
group-by	group_by
apply	-	Use the f(*args) construct.
not-empty	-
some	some
seq?	is_seq
every?	every
not-every?	not_every
not-any?	not_any
empty?	-
empty	empty
doseq	-	Use for … in.
dorun	dorun
doall	-	Use Python’s list.
realized?	-
seq	-	Use Python’s list.
vals	-	Use Python’s dict.values.
keys	-	Use Python’s dict.keys.
rseq	-
subseq	-
rsubseq	-
repeatedly	repeatedly
iterate	iterate
repeat	repeat	(repeat n x) becomes repeat(x, n). Equivalent to itertools.repeat.
range	range	Prefer Python’s range for everything but infinite generators.
line-seq	-	Loop over an io.BufferedReader.
resultset-seq	-
re-seq	-	Use Python’s re.finditer.
tree-seq	tree_seq
file-seq	-	Use Python’s os.walk.
xml-seq	-
iterator-seq	-
enumeration-seq	-
hash-map	-	Use Python’s dict.
array-map	-	Use Python’s dict.
sorted-map	-	Use collections.OrderedDict.
sorted-map-by	-
hash-set	-	Use Python’s set.
set	-	Use Python’s set.
sorted-set	-
sorted-set-by	-
dedupe	dedupe

We also implemented count, which uses Python’s len when possible and fallbacks on a for loop for other cases.

Functions

We also provide miscellaneous functions as well as functions that work on functions.

Clojure	clj	Comment
identity	identity
partial	-	Use Python’s functools.partial
comp	comp
complement	complement
constantly	constantly
juxt	juxt
distinct?	is_distinct

Clojure	clj	Comment
inc	inc
dec	dec