Creating a Python lambda function from a string sequence

Question

I have a list of m elements and n different numbers that appear in a list of strings. The list follows the following format example

eq = ['12', '2', '3', '-123', '-1', 'X']

Note, X represents the constant 1, other than the variable 1. I want to be able to convert this to a lambda function that takes in a list x and acts like this list was summed together. For our example the function would be

f(x) = x[1]*x[2] + x[2] + x[3] - x[1]*x[2]*x[3] - x[1] + 1

I know how to do this with a normal function, but I wanted to get it to work with a lambda and hit a wall. Any help would be appreciated!

Here is the function that works for the problem:

def evaluateList(x, lst):
    num = 0
    for term in lst:
        if term[0] == "X":
            num += 1
        elif term[0] == "-":
            num -= reduce(lambda x,y: x*y, [x[int(y)-1] for y in term[1:]])
        else:
            num += reduce(lambda x,y: x*y, [x[int(y)-1] for y in term])
    return num

Answer 1

I think this is simple enough:

from operator import mul
from functools import reduce
prod = lambda L: reduce(mul, L, 1)
evaluateList = lambda(x, eq): sum(
    1 if expr == 'X' 
    else prod(-1 if i == '-' 
              else x[int(i)] 
              for i in expr) 
    for expr in eq)