8.11. Exercises: Strings

The exercises have been broken up into three parts. There are five replit pages with starter code for you to fork. Most sections have replit starter code provided. You should see links to your starter code above the exercise steps.

8.11.1. Part One: Bracket Notation

8.11.1.1. Points to Ponder

Identify the result for each of the following statements:

There’s no starter code for this one, just try it on your own with old-fashioned pencil and paper!

  1. 'Characters'[8]

  2. "Strings are sequences of characters."[5]

  3. len("Wonderful")

  4. len("Do spaces count?")

8.11.1.2. Bracket Notation Basics

The starter code for this and the following part can be found at repl.it.

Use bracket notation to:

  1. Print a slice of the first 12 characters from "Strings_are_sequences_of_characters."

  2. Print a slice of the last 12 characters from the same string. You should NOT have to count the index values yourself!

  3. Print a slice of the middle 12 characters from the same string.

Check Your Solutions

8.11.1.3. Looping Through a String

Use index values to loop backwards through a string:

  1. First, print one letter per line.

  2. Next, instead of one letter per line, use the accumulator pattern to build up and print the reversed string. For example, if given the string 'good', your program prints doog.

  3. Finally, use concatenation to print the combination of the original and reversed string. For example, given the string 'tomato', your program prints tomatootamot. (If you want to be fancy, include the | character to make the output look almost like a mirrored image: tomato | otamot).

Check Your Solutions

8.11.2. Part Two: String Methods and Operations

8.11.2.1. String Methods and Data Types

Code it at repl.it.

The len() function returns the number of characters in a string. However, the function will NOT give us the length of an integer. If num = 1001, then len(num) throws an error instead of returning 4.

  1. Use str() to change num from an int to a string data type.

  2. Print the length (number of digits) in num.

  3. Modify your code to print the number of digits in a float value (e.g. num = 123.45 has 5 digits but a length of 6). The digit count should NOT include the decimal point.

  4. What if num could be EITHER an integer or a decimal? Add an if/else statement so your code can handle both cases. (Hint: Consider using the find() method or the in operator to check if num contains a decimal point).

Check Your Solutions

8.11.2.2. Loops, Conditionals, and Strings! Oh my!

Code it at repl.it.

Given word = 'bag':

  1. Set up a loop to iterate through the string of lowercase vowels, 'aeiou'.

  2. Inside the loop, create a new string from word, but with a different vowel. Use the replace() string method.

  3. Print the new string.

    Properly done, your output should look something like this:

    bag
beg
big
bog
bug

  4. Try other words besides 'bag'!

Check Your Solutions

8.11.2.3. Method Chaining Fun with DNA

Code it at repl.it.

Consider a string that represents a strand of DNA: dna = " TCG-TAC-gaC-TAC-CGT-CAG-ACT-TAa-CcA-GTC-cAt-AGA-GCT    ". There are some typos in the string that you need to fix:

  1. Use the strip() method to remove the leading and trailing whitespace, and then print the result.

  2. Change all of the letters in the DNA string to UPPERCASE and print the result.

  3. Note that you need to reassign the changes back to the dna variable in order to see them printed. Apply these fixes to your code so that print(dna) prints the DNA strand in UPPERCASE with no whitespace.

  4. Let’s use string methods to do more work on the same DNA strand:

    1. Use replace() to remove the sequence 'GCT', and then print the altered strand. Don’t forget about the extra hyphen!

    2. Look for the sequence 'CAT' with find(). If found print, 'CAT found', otherwise print, 'CAT NOT found'.

    3. Use count() to find the number of hyphens (-) in the string, then print the number of genes (in this case, a gene is a set of 3 letters) in the DNA strand. Note that the number of genes will be 1 more than the number of hyphens.

    4. Finally, use an f-string to print the output "The DNA string is ___ characters long and contains ___ genes." Fill in the blanks with the length of the string and the number of genes.

Check Your Solutions

8.11.3. Part Three: String Formatting

8.11.3.1. Template Literals

Code it at repl.it.

Assign your favorite, school-appropriate number and word to two variables.

  1. Use format() and index values to print the string, "Here is my number: ___, and here is my word: ___, and here is my number again: ___."

  2. Print the string, "Here is my word 3 times: ___/___/___, and here is my number squared: ___."

Check Your Solutions

8.11.3.2. Debugging Practice

No starter code for this one.

The following code sample works, but it can be improved.

  1. Assuming that advice remains a string, when will the code produce the wrong output?

  2. Why will the code do this?

  3. What should the programmer do to fix the code?

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advice = "Don't Panic"

output = "The text, '{0}' contains {1} characters."

print(output.format("Don't Panic", 11))

Console Output

The text, 'Don't Panic' contains 11 characters.

Check Your Solutions

8.11.4. Submitting Your work

When finished copy the URLs to your repls for the exercises, separating each URL with a semi-colon and paste them into the submission box in Canvas for Exercises: Strings and Lists and click Submit.

You should have a total of 9 repls, 5 from the above String Exercises and 4 from the List Exercises