How can I substitute a list by index in python?

Question

I need to write a function that contains 3 input parameters:

• A list called randome containing random integer numbers

• A list called indexes that contains (non-negative) indexes of items that need substitution by the third parameter. It is possible that indexes contains non-existent indexes for source. Check if the index actually exists in source before you substitute. Perhaps using the len of randome?

• A value new_value that we use to overwrite the items in source. Assign True as default value.

For example: substitution_function([1, 2, 3, 4, 5], [0, 2], True) must return this list: [True, 2, True, 4, 5]

Anyone have any ideas?

def substitution_function(randome, indexes, new_value=True):

    result = []
    for data in indexes:
        if data <= len(source):
            result.append(new_value)
        else:
            for i in range(len(source)):
                result.append(source[i])    
    return result

But this code can be greatly improved

Answer 1

It runs for loop on randome with getting item's index by enumerate(). If index is in indexes it returns new_value to listcomp's list if it's not it returns item. The possible problem of spare indexes in indexes is solved by just not touching them at all.

def substitution_function(randome, indexes, new_value=True):
    return [new_value if e in indexes else i for e,i in enumerate(randome)]

Answer 2

I think it's better to you read the Stack Overflow Guidelines 😎

def overwriteArr(arr, idxs, val):
    for idx in idxs:
        try:
            arr[idx] = val
        except:
            pass
    return arr

print(overwriteArr([1, 2, 3, 4, 5], [0, 2], True)) # [True, 2, True, 4, 5]

Answer 3

The way you started is strange, let's start from scratch. There is 2 ways

1. Replace with the given value, at the given indexes

   def substitution_function(source, indexes, new_value=True):
       for index in indexes:
           if index < len(source):
               source[index] = new_value
       return source
   

2. Build a whole new list, and conditionally use original value or replacement one

   # that solution is safe-proof to invalid index
   def substitution_function(source, indexes, new_value=True):
       result = []
       indexes = set(indexes) # can be added in case of large list
       for i, data in enumerate(source):
           if i in indexes:
               result.append(new_value)
           else:
               result.append(data)
       return result