Gotchas

Objects changed in place

Each line shows the values its variables had when that line ran, even if a name is assigned again later. Values are not copied, though: an object that is changed in place afterwards (xs.append(4), arr[0] = 5 on a numpy array) shows its final contents on every line. Make a new object instead (xs = xs + [4]), or give each quantity its own name.

Jupyter cells can run out of order

In a notebook, %%render reads values from the notebook’s namespace. If you run cells out of order, or re-use a name in a later cell, a rendered cell can show values that are beautifully formatted and wrong. Before you rely on a notebook, restart the kernel and run all cells from the top.

Not all Python is rendered

handcalcs renders arithmetic, function calls, comparisons, conditional expressions, conditionals and loops. It leaves out function and class definitions, while loops, with blocks, augmented assignments and print() calls. See What is not rendered.

Floor division and modulo

// and % are rendered (LaTeX shows // with floor brackets), but readers may not recognise them in a hand calculation. Consider floor(a / b) for clarity.

Responsibility for results

handcalcs is free, open-source software provided without warranty. If you use it for work that may become a legal document, such as engineering design calculations, you are responsible for checking that the results are what you expect. The point of showing the substitution is to make that check easy.