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An Association List construct

Project description


An Association List construct for Python


pip install alistpy


This simple library provides an AList object that should be a drop-in replacement for most dictionaries, but based on immutable data structures instead.

Cheap to construct, expensive to mutate, as it isn't mutable. Every mutative method actually generates a new AList in it's place.


import alist

# This is cheap:
a = alist.AList(x=0,y=1)

# This is also cheap:

# This is expensive:
a['x'] = 12

Differences to Dictionaries

There's primarily two differences:

  • Mutating the AList is expensive, rather than cheap.

  • Setting the same key multiple times at init time is a ValueError.

That is, Python is happy with:

{'x': 0, 'x': 4}
> {'x': 4}

That sort of behaviour might be unexpected, or cause unexpected problems for the programmer.

So, instead alist:

alist.AList(x=0, x=4)
> Exception raised, ValueError


Issue tracker.

Anonymous users (those without accounts) are welcome to submit issues.

Explicit API

There isn't one yet.

Check back in future versions. For now, be guided by the tests.


Install pytest, and then run it.

Currently 31 tests for 21 methods.


BSD-3 Clause. See for more.

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