Reliability: Path/Cut Vector Technique in Python

Question

I have a list, lst , that contains only 0's and 1's of length n .

The list represents either a cut vector or a path vector, from reliability analysis, which may or may not be minimal cut/path vectors themselves.

The elements within the list represent separate variables, say x1 , x2 , and x3 and the length of the list, n , represents the number of variables being represented.

For example, the list [0, 1, 1] represents 3 variables, x1 , x2 , and x3 .

Given the input, lst , I want to return a list or string that is guided by the following rules.

Rules:

1. If x _i = 1:

   a. return (x _i )

2. else if x _i = 0:

   b. return: (1 - x _i )

Examples:

[0, 1] => [1-X1, X2] or "1-X1, X2"

[1, 0] => [X1, 1-X2] or "X1, 1-X2"

[0, 1, 1] => [1-X1, X2, X3] or "1-X1, X2, X3"

[1, 1, 1] => [X1, X2, X3] or "X1, X2, X3"

My Code:

def get_function(path_vector):
    lst = []
    for item in path_vector:
        if "0" in item:
            print("1-", item, sep="")
            lst.extend(["1-", item])
        else:
            print(item)
            lst.append(item)
    print(lst)
    expr = "*".join(lst)
    return expr

Goal:

The eventual goal is to join the items in the new list - separated by a * - and input them into a function from the sympy library.

Any tips are appreciated.

Answer 1

item has values 0 or 1 but you need its position on list to create string 1-X{position} or X{position}

You may use enumarate(..., 1) to get its position on list.

Because you have integer values then you should compare integers if item == 0:

---

Minimal working code which use list examples to generate string and compare with expected result

def get_function(path_vector):
    lst = []

    for position, item in enumerate(path_vector, 1):
        if item == 0:
            text = f"1-X{position}" 
        else:
            text = f"X{position}" 
        lst.append(text)
        print('text:', text)

    print('lst:', lst)
    expr = "*".join(lst)

    return expr
    
# --- main --- 
    
examples = [    
    ([0, 1], "1-X1*X2"),
    ([1, 0], "X1*1-X2"),
    ([0, 1, 1], "1-X1*X2*X3"),
    ([1, 1, 1], "X1*X2*X3"),
]

for data, expected_result in examples:
    result = get_function(data)
    print(data, expected_result, result, expected_result==result)