A simple lazy Python Calculation Engine.

The module is still in development. You can install it by cloning this repository and using the poetry install command.

git clone [email protected]:bsdz/calcengine.git
cd calcengine
python3 -mvenv --prompt calceng .venv
. ./.venv/bin/activate
poetry install

Alternatively, you can add to your existing poetry project:

poetry add git+https://github.com/bsdz/calcengine.git

Or install via pip:

pip install git+https://github.com/bsdz/calcengine.git#master

The core module for the calculation engine only uses core python standard library.

The demo spreadsheet application uses pyqt5, pandas, matplotlib and pillow.

First instantiate a CalcEngine and use watch decorator to register functions as nodes. Note that a function along with any arguments and keyword arguments make a unique node.

from calcengine import CalcEngine

ce = CalcEngine()

@ce.watch()
def a():
    print("..in a")
    return 100

@ce.watch()
def b():
    print("..in b")
    return a() 

@ce.watch()
def c(x, y):
    print(f"..in c with x={x} and y={y}")
    return 2 * a() + x * y

@ce.watch()
def d(x, y=0):
    print(f"..in d with x={x} and y={y}")
    return 3 * b() + x - y

@ce.watch()
def e():
    print("..in e")
    _x = d(5, y=-3)
    return c(2, 3) - 5 + _x

@ce.watch()
def f():
    print("..in f")
    return d(0) + e()

Calling a function will cache all values and path during first run.

>>> f()
..in f
..in d with x=0 and y=0
..in b
..in a
..in e
..in d with x=5 and y=-3
..in c with x=2 and y=3
809

And obviously a 2nd invocation will retrieve the final value from cache.

>>> f()
809

Invalidating a node by calling function helper method.

>>> e.invalidate()
>>> f()
..in f
..in e
809

Invalidating a node without arguments if previous call did have arguments won't have any effect.

>>> d.invalidate()
>>> f()
809

Whereas with arguments specified exactly as prior call will. Note the sensitivity of argument specification.

>>> d.invalidate(5, y=-3)
>>> f()
..in f
..in e
..in d with x=5 and y=-3
809

It is also possible to add a trigger that will be called on completion of a function. This might be used to produce some form of data binding in applications.

def my_trigger(res):
    print(f"got {res}")

>>> c.node_calculated.append(my_trigger)
>>> c.invalidate(2, 3)
>>> f()
call f
call e
call c with x=2 and y=3
got 206
809

Included is a simple spreadsheet demo. Read more here

To install the dependencies required by the demo. When cloning this repo also include the "demo" extras.

poetry install -E demo
python demo/spreadsheet/main.py

• Support watching global variables.
• Support multiprocessing.
• Support asyncio?.

Some similar packages spotted. None of them tested.

• pyungo
• dask
• schedula
• graphkit
• mdf