Stretch tasks Lists, Strings and Files in Python

Round 1: Quiz Blitz

1. 18 Index -1 is the last item.
2. 4 Indexes start at 0, so the last is len - 1.
3. Com A slice stops before the second index: characters 0, 1 and 2.
4. Whitespace, including the newline, from both ends Forgetting it is why values read from a file often fail to match.
5. "a" "a" appends. "w" empties the file first.
6. False Write mode empties the file before anything is written.
7. 15 split makes the list ['Amira', '15', 'Year 10'].
8. A string Every time, so numbers must be cast.
9. 0 Row 1 is [0, 1, 0], and position 2 in it is 0.
10. 65 ord gives the character code. chr converts back.
11. append(); insert() append adds to the end. insert adds at a position.
12. It closes the file for you, even if something goes wrong It is the safer form.

Round 2: Quick Fire

1. • The highest index is 2, but the loop goes one too far
   • Remove the + 1, or loop over the items
   Model answer

   The list has 3 items, so its highest index is 2, but range(len(scores) + 1) goes up to 3, one too far, which raises an IndexError. Remove the + 1, so the loop is for i in range(len(scores)):, or loop over the items with for score in scores:.

2. • Each line still ends with a newline character
   • strip() removes it
   Model answer

   Each line read from a file still ends with a newline character, so the value is "Amira" followed by a newline, not "Amira". Calling strip() removes the newline so the comparison works.

3. • "w" empties the file first, destroying what was there
   • "a" adds to the end, keeping the existing contents
   Model answer

   Write mode, "w", empties the file before anything is written, so the existing contents are destroyed. Append mode, "a", adds the new data to the end and keeps what is already there.

4. • Everything read from a text file is a string
   • Adding a string to a number fails
   Model answer

   Everything read from a text file is a string, so the score is the text "18", not the number 18. Adding a string to a number total raises a TypeError, so int() must convert it first.

Round 3: Big Think

1. • Open the file
   • Loop through each line
   • strip each line
   • split it at the comma
   • Cast the score to an integer
   • Compare it with the best so far
   • Remember the name that goes with it
   • Print the name after the loop
   Model answer

   PythonCopy

   best_score = -1
   best_name = ""
   with open("scores.txt", "r") as file:
       for line in file:
           parts = line.strip().split(",")
           score = int(parts[1])
           if score > best_score:
               best_score = score
               best_name = parts[0]
   print(best_name)

2. • A list holds many results under one name
   • append adds each new result
   • A loop works through the list, such as to total the scores
   • A file makes the results persist between runs
   • Append mode keeps earlier results, while write mode wipes them
   • Each result is written as one line
   • Reading back uses strip and split
   • Scores are cast with int before arithmetic
   Model answer

   During the lesson, the results are held in a list, which stores many values under one name, and append adds each new result. A for loop works through the list to total the scores and find the average. A list disappears when the program closes, so the results are saved to a file, which makes them persist between runs. Each result is written as one line, such as Amira,18, using append mode so earlier results are kept; write mode would wipe them. Next lesson, the program reads the file back, using strip to remove each newline and split to separate the name from the score, then int to convert the score before doing arithmetic.

This or That

1. 5 len counts the items. The highest index is 4.
2. C Indexing starts at 0.
3. No: it stops before 3 Like range, a slice stops before the second number.
4. "a" "w" empties the file first. "a" appends to the end.
5. split strip removes whitespace. split divides a string at a separator.
6. The row The first index selects the row, the second the position within it.
7. B chr turns a code back into its character, and 65 is A.
8. for score in scores Loop over the items when you only need the values.

Memory Match

• A 6 Index: Position, counted from 0
• B 4 Slice: A section that stops before the second index
• C 2 split: Divides a string at a separator
• D 1 strip: Removes whitespace from both ends
• E 3 len: Counts the items in a list
• F 5 Append mode: Opens a file to add to its end

Sort It

1. String word.find("put") find searches a string.
2. File file.readlines() Reading every line of a file.
3. File file.write("Ben,14\n") Writing a line to a file.
4. String line.split(",") split divides a string into a list.
5. List scores.pop() pop removes an item from a list.
6. File open("scores.txt", "a") Opening a file in append mode.
7. List scores.sort() sort puts a list in order.
8. File for line in file: Looping through a file line by line.
9. String word.strip() strip removes whitespace from a string.
10. String word.upper() upper changes the case of a string.
11. List board[1][2] Row then position in a 2D list.
12. List scores.append(25) append adds an item to the end of a list.