Question

#We've started a recursive function below called #measure_string that should take in one string parameter, #myStr, and returns its length. However, you may not use #Python's built-in len function. # #Finish our code. We are missing the base case and the #recursive call. # #HINT: Often when we have recursion involving strings, we #want to break down the string to be in its simplest form. #Think about how you could splice a string little by little. #Then think about what your base case might be - what is #the most basic, minimal string you can have in python? # #Hint 2: How can you establish the base case has been #reached without the len() function? #You may not use the built-in 'len()' function.

Answer 1

Answer:

Here is the Python program:  

def measure_string(myStr): #function that takes a string as parameter  

 if myStr == '': #if the string is empty (base case)  

      return 0  #return 0  

  else: #if string is not empty  

      return 1 + measure_string(myStr[0:-1]) #calls function recursively to find the length of the string (recursive case)  

#in order to check the working of the above function the following statement is used    

print(measure_string("13 characters")) #calls function and passes the string to it and print the output on the screen      

Explanation:

The function works as following:  

Suppose the string is 13 characters  

myStr = "13 characters"  

if myStr == '': this is the base case and this does not evaluate to true because myStr is not empty. This is basically the alternate of  

if len(myStr) == 0: but we are not supposed to use len function here so we use if myStr == '' instead.  

So the program control moves to the else part  

return 1 + measure_string(myStr[0:-1])  this statement is a recursive call to the function measure_string.  

myStr[0:-1] in the statement is a slice list that starts from the first character of the myStr string (at 0 index) to the last character of the string (-1 index)  

This statement can also be written as:  

return 1 + measure_string(myStr[1:])

or  

return 1 + measure_string(myStr[:-1])  This statement start from 1st character and ends at last character  

This statement keeps calling measure_string until the myStr is empty. The method gets each character using a slice and maintains a count by adding 1 each time this statement is returned.The function breaks string into its first character [0:] and all the rest characters [:-1]. and recursively counts the number of character occurrences and add 1. So there are 13 characters in the example string. So the output is:  

13