Please explain

DNA is a large molecule that can be abstractly defined as a sequence of nucleotides including Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). A DNA sequence is a representation of a string of these four nucleotides, e.g. ATTCGTAACTAGTAAGTT. DNA sequencing is the process of identifying the sequence of nucleotides in a strand of DNA. This is a critical task for understanding human genomic variation and the genetic contributions to certain diseases. The human genome has about 3 billion nucleotides. DNA sequencing is a computationally intensive task that needs efficient string pattern and substring matching algorithms. And in the first two questions of the assignment, you are asked to write a program called SubstringFinder1 to find a substring with defined characteristics in a given string. SubstringFinder1 works as follows: - Takes a string called source as the first input. - Takes a positive integer k as the second input. SubstringFinder1 assumes the user provides a number greater than zero. - SubstringFinder1 does the processing and prints the k-length substring of source with the greatest number of unique characters. - If there are multiple substrings that satisfy the condition in the previous step, SubstringFinder1 prints the one that appears first in the user-provided string, source. - SubstringFinder1 continues to get inputs from the user until the user enters 'quit' for string source. You are not allowed to use any Python built-in methods (introduced in slide 16 of lecture 5.1) or user-defined modules in developing SubstringFinder1. You can see examples of SubstringFinder1 input and output in Table 1. Note that your program input and output format should be exactly the same as the format of the examples shown in Table 1