components = {
    "U1": ("0Ohm", "10V", "IU1"),
    "R1": ("1e3Ohm", "UR1", "IR1"),
    "R2": ("5e3Ohm", "UR2", "IR2"),
}
nodes = {"n1", "n2"}
connections = {
    "U1": ["n1"],
    "n1": ["R1", "R2"],
    "R1": ["n2"],
    "R2": ["n2"],
    "n2": ["U1"],
}
nodeCoeffs = {}
for n in nodes:
    nodeCoeffs[n] = [
        f"-{components[k][2]}" if n in v else f"{components[x][2]}"
        for k, v in connections.items()
        for x in v
        if k == n or n in v
    ]


print(nodeCoeffs)