Qwery List

QList is a small library introducing a new way to use higher order functions with lists, with lazy evaluation. It also aims to address ugly python list methods such as map, filter and reduce. Whoever invented this:

xs = ['1', '2', '3', '4']
s = reduce(lambda acc, x: acc + x, filter(lambda x: x < 3, map(int, xs)), 0)

must reevaluate their life choices (yes, I am being cocky and most likely dumdum) but listen to me first and look what the world of lazy evaluation has to offer!

xs = QList(['1', '2', '3', '4'])
s = xs.map(int).filter(lambda x: x < 3).fold(lambda acc, x: acc + x, 0)

As a bonus you get len() method, so no longer will you be forced to wrapp your lists in this type of code len(xs) and simply call xs.len() (I understand it is negligibly slower but look how much nicer it looks!)

Quick tutorial

Let's say we want to read numbers from a file and choose only the even ones. No problem at all!

from qwlist import QList

with open('path/to/file.txt', 'r') as file:
    qlist = QList(file.readlines())
even = qlist.map(int).filter(lambda x: x % 2 == 0).collect()

Why is there this collect at the end? Because all operations on the QList are lazy evaluated, so in order to finally apply all the operations you need to express that.

There is also an eagerly evaluated EagerQList in case all the actions performed on the list should be evaluated instantaneously. This object is in the qwlist.eager module, but it is also possible to transform QList into EagerQList simply by calling eager()

>>> from qwlist import QList
>>> QList(range(3)).eager().map(str)
['0', '1', '2']

EagerQList has the same methods that QList has (filter, map, foreach, ...) but not lazy evaluated so there is no need to call collect at the end.

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Examples

Making QList from an iterable

>>> QList([1, 2, 3, 4])
[1, 2, 3, 4]

Making QList from a generator

>>> QList(range(3))
[0, 1, 2]

Making a list of pairs: int and str

>>> qlist = QList([1, 2, 3])
>>> qlist.zip(qlist.map(str)).collect()
[(1, '1'), (2, '2'), (3, '3')]

Summing only the even numbers

>>> QList(range(10)).filter(lambda x: x % 2 == 0).fold(lambda acc, x: acc + x, 0)
20

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Side note

This syntax resembles Rust syntax:

Rust	Python
let xs = vec![1, 2, 3, 4]; let double_xs: Vec<i32> = xs.iter().map(|&x| x * 2).collect(); println!("{double_xs:?}"); // [2, 4, 6, 8]	xs = QList([1, 2, 3, 4]) double_xs = xs.map(lambda x: x * 2).collect() print(double_xs) # [2, 4, 6, 8]

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Story behind this whole idea

Prime idea? Vicious mockery!
During studying, I had to do a lot of list comprehensions in Python, alongside methods such as map or filter and although they are quite powerful, using them in Python is just annoying. Combining them makes you read the code in an unnatural order going from right to left. That is the main reason that for a long time I preferred simple for-loops as opposed to using mentioned methods. Until one day my teacher asked the whole class why no one is using list comprehensions and higher order functions.
"Do you guys know python?" he asked tendentiously.
"I would use those functions if they were nicer" I thought.
During that period I also learnt Rust and immediately fell for it. Especially with how convenient it is to replace for-loops with method calls. And that's how the idea for a python package qwlist was born.

I hereby announce that UwU, Qwery Listwu!