lambdify sympy with Variable-Length Arguments

Question

I have a list of expr with a different number of variables as follows:

G = [[-x_1 + y_1], [-x_2 + y_1 + y_2], [y_1 + y_2] , [-y_3] , ....]

I want to evaluate these expressions using sympy and lambdify. For this purpose, I have written the following instructions:

def f(item):
    return lamndify(list(tem.free_symbols), item)



for  item in G:
    f_ = f(item)
    ...

Now, what should I do to call f_ because there are different variables in each term?

score 1 · Accepted Answer · answered Feb 01 '22 at 13:57

Get the pertinent free_symbols, too. Perhaps make your function return those for you or else recapture them:

def f(item):
    return lambdify(list(item.free_symbols), item)
def f2(item):
    args = list(item.free_symbols)
    return args, lambdify(args, item)

for [gi] in G:
    args = list(gi.free_symbols)
    f_ = f(gi)
    a, f2_ = f2(gi)
    assert f_(*args) == f2_(*a)

If you have a set of values you want to use like vals = {x_1:1,x_2:2,y_1:3,y_2:4,y_3:5} then something like this could be used:

>>> for [gi] in G:
...     a, f2_ = f2(gi)
...     v = [vals[i] for i in a]
...     print(v, f2_(*v))
...
[3, 1] 2
[3, 2, 4] 5
[3, 4] 7
[5] -5

lambdify sympy with Variable-Length Arguments

1 Answers1