Python list comprehensions in MATLAB

My classes this semester are requiring a whole lot MATLAB, with its …unusual syntax and focus on matrices over loops.

I was pretty excited to find out MATLAB has some basic support for python calling.

I got right to work on getting list comprehensions, a feature I’m dearly missing.

function array = pylist(statement, vars)
    workspace = py.dict;
    for v = 1:length(vars)
        update(workspace, py.dict(pyargs(cell2mat(vars(v)), evalin('caller', cell2mat(vars(v))))))
    cell2mat(cell(py.eval(statement, workspace)))


The function takes a string python expression and a cell array of variable names to pass in, and returns an array of the results.

>> x = 6

x =


>> pylist('[q**2 for q in range(int(x))]', {'x'})

ans =

	0	1	4	9	16	25

There’s some cool bits going on here, especially with the variable loading. MATLAB exposes the current workspace through evalin(), letting us fetch variables by name. x needs int casting because it’s comes out as a float. Most of the code is in processing the python data type wrappers.

Of course, the minute I finished this I realized MATLAB has its own alternative to list comprehensions, with the function arrayfun().


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