Question

#Write a function called fancy_find. fancy_find should have #two parameters: search_within and search_for. # #fancy_find should check if search_for is found within the #string search_within. If it is, it should print the message #"[search_for] found at index [index]!", with [search_for] #and [index] replaced by the value of search_for and the #index at which it is found. If search_for is not found #within search_within, it should print, "[search_for] was #not found within [search_within]!", again with the values #of search_for and search_within. # #For example: # # fancy_find("ABCDEF", "DEF") -> "DEF found at index 3!" # fancy_find("ABCDEF", "GHI") -> "GHI was not found within ABCDEF!"

Answer 1

Answer:

Here is the Python program:

def fancy_find(search_within , search_for):  # function definition of fancy_find function that takes two parameters

   index = 0  #to store the index of search_within where the search_for string is found

   if search_for in search_within:  #checks if the string search_for is present in string search_within

       sf = search_for[0]  #points to the first character of the search_for

       for sw in search_within:  #iterates through search_within

           if sw == sf:  #if the first character of search_for is equal to the character at sw index of search_within

               if search_within[index:index+len(search_for)] == search_for:  #checks if the value of search_for is found in search_within

                   print(search_for,"found at index",index,"!")  #if above condition is true prints the message "[search_for] found at index [index]!", with [search_for] and [index] replaced by the value of search_for and the index at which it is found

                   return ""  

           index += 1  #increments value of index at each iteration

   print(search_for,"is not found within", search_within)  #if search_for is not found within search_within, prints message "[search_for] was not found within [search_within]!" with the values of search_for and search_within.

   return ""    

#following two statements are used to test the working of above function

print(fancy_find("ABCDEF", "DEF"))  #calls fancy_find() passing "ABCDEF" as search_within and "DEF" as search_for

print(fancy_find("ABCDEF", "GHI")) #calls fancy_find() passing "ABCDEF" as search_within and "GHI" as search_for

Explanation:

The program is well explained in the comments. I will explain the working of the function with the help of an example:

Suppose

search_within = "ABCDEF"

search_for = "DEF"

We have to find if search_for i.e. DEF is present in search_within i.e. ABCDEF

if search_for in search_within statement checks using in operator that if DEF is included in ABCDEF. Here this condition evaluates to true so the next statement sf = search_for[0]  executes which sets the first element of search_for i.e. D to sf. So sf = 'D'

for sw in search_within this statement has a for loop that iterates through ABCDEF and works as following:

At first iteration:

sw contains the first character of search_within  i.e. A

if sw == sf: condition checks if the first character of the search_for i.e. D is equal to sw i.e. A. Its not true so the program control moves to this statement:

index += 1 This increases the value of index by 1. index was initialized to 0 so now it becomes 1. Hence index=1

At second iteration:

sw contains the second character of search_within  i.e. B

if sw == sf: condition checks if the first character of the search_for i.e. D is equal to sw i.e. B Its not true so the program control moves to this statement:

index += 1 This increases the value of index by 1. index was initialized to 0 so now it becomes  2. Hence index=2

At third iteration:

sw contains the third character of search_within  i.e. C

if sw == sf: condition checks if the first character of the search_for i.e. D is equal to sw i.e. C Its not true so the program control moves to this statement:

index += 1 This increases the value of index by 1. index was initialized to 0 so now it becomes  3. Hence index=3

At fourth iteration:

sw contains the third character of search_within  i.e. D

if sw == sf: condition checks if the first character of the search_for i.e. D is equal to sw i.e. D. Its true so so the program control moves to this statement:

  if search_within[index:index+len(search_for)] == search_for:

current value of index=3

len(search_for) returns the length of DEF i.e. 3

So the if condition checks for the search_for in search_within. The statement becomes:

if search_within[3:3+3] == search_for:

search_within[3:3+3]  means from 3rd index position of search_within to 6-th index position of the search_within. This means from 4th element of search_within i.e. D to the last. Hence search_within[3:3+3] is equal to DEF.

search_for = DEF so

if search_within[3:3+3] == search_for: checks if

search_within[3:3+3] = DEF is equals to search_for = DEF

Yes it is true so

print(search_for,"found at index",index,"!") statement is executef which prints the following message:

DEF found at index 3!

This output is because search_for = "DEF" and index=3