Iterating over strings in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each character in the string.

Python

for char in [1]:
    print(char)

Drag options to blanks, or click blank then click option'

A"hello"

B12345

C['h', 'e', 'l', 'l', 'o']

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the string.

Using a list instead of a string.

The string must be in quotes to be treated as a string. So "hello" is correct.

2fill in blank

medium

Complete the code to count how many times 'a' appears in the string.

Python

count = 0
for char in "banana":
    if char == [1]:
        count += 1
print(count)

Drag options to blanks, or click blank then click option'

A'b'

Ba

C"a"

D'a'

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes instead of single quotes (both work but only one is correct here).

Not using quotes at all.

We check if the character equals the letter 'a' using single quotes.

3fill in blank

hard

Fix the error in the code to print each character in the string.

Python

word = "code"
for [1] in word:
    print(char)

Drag options to blanks, or click blank then click option'

Aword

Bchar

Cletter

Dc

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name in the loop and print statement.

Using the string name as loop variable.

The loop variable must be named 'char' to match the print statement.

4fill in blank

hard

Fill both blanks to create a dictionary with letters as keys and their uppercase as values.

Python

result = { [1]: [2] for [1] in "abc" }

Drag options to blanks, or click blank then click option'

Achar

Bchar.upper()

Cletter

Dletter.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for key and loop variable.

Not calling upper() method correctly.

Use 'char' as the loop variable and 'char.upper()' to get uppercase letters.

5fill in blank

hard

Fill all three blanks to create a dictionary with letters as keys, their index as values, but only for letters after 'b'.

Python

result = { [1]: [2] for [1], [2] in enumerate("abcde") if [3] > 1 }

Drag options to blanks, or click blank then click option'

Aletter

Bindex

Didx

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up index and letter variables.

Using wrong variable names in the if condition.

Use 'letter' and 'index' from enumerate, and filter where index > 1.

Practice

1. What does the following code do?
for letter in "hello":
print(letter)

easy

A. Prints each letter of the word 'hello' on a new line

B. Prints the whole word 'hello' once

C. Prints the length of the word 'hello'

D. Causes an error because strings can't be looped

Solution

1. Step 1: Understand the for loop over a string

   The loop goes through each character in the string "hello" one by one.

2. Step 2: Print each character

   Inside the loop, each letter is printed on its own line.

3. Final Answer:

   Prints each letter of the word 'hello' on a new line -> Option A

4. Quick Check:

   Loop over string prints letters individually [OK]

Hint: For loops over strings print letters one by one [OK]

Common Mistakes:

• Thinking the whole string prints at once
• Confusing string length with letters
• Believing strings can't be looped

2. Which of the following is the correct syntax to loop over each character in the string text?

easy

A. for char to text: print(char)

B. for char in range(text): print(char)

C. for char in text: print(char)

D. for i in text.length: print(i)

Solution

1. Step 1: Identify correct for loop syntax for strings

   In Python, to loop over characters in a string, use for variable in string:.

2. Step 2: Check each option

   for char in text:
print(char) uses correct syntax. The other options use invalid syntax like 'to' instead of 'in', range() on a string, or non-existent .length attribute.

3. Final Answer:

   for char in text:
   print(char) -> Option C

4. Quick Check:

   Correct for loop syntax over string is for char in text:
   print(char) [OK]

Hint: Use 'for char in string:' to loop letters [OK]

Common Mistakes:

• Using range() on a string directly
• Trying to use .length instead of len()
• Using incorrect loop keywords

3. What is the output of this code?

word = "code"
result = ""
for ch in word:
    result += ch.upper()
print(result)

medium

A. code

B. CODE

C. Code

D. cODe

Solution

1. Step 1: Loop through each letter in 'code'

   The loop takes each character: 'c', 'o', 'd', 'e'.

2. Step 2: Convert each letter to uppercase and add to result

   Each letter is changed to uppercase ('C', 'O', 'D', 'E') and added to the empty string result.

3. Final Answer:

   CODE -> Option B

4. Quick Check:

   Uppercase each letter and join = CODE [OK]

Hint: Uppercase letters inside loop to build new string [OK]

Common Mistakes:

• Not converting letters to uppercase
• Printing original string instead of result
• Using += without initializing result

4. Find the error in this code:

text = "hello"
for i in text:
    print(text[i])

medium

A. Variable 'text' is not defined

B. Missing colon after for loop

C. Loop should be 'for i in range(text):'

D. Using 'i' as index causes TypeError

Solution

1. Step 1: Understand the loop variable 'i'

   Here, 'i' takes each character from 'text', so 'i' is a letter, not an index.

2. Step 2: Using 'text[i]' causes error

   Since 'i' is a letter, using it as an index causes a TypeError because string indices must be integers.

3. Final Answer:

   Using 'i' as index causes TypeError -> Option D

4. Quick Check:

   Loop variable is letter, not index, so indexing fails [OK]

Hint: Loop variable is letter, not index; use range(len(text)) for indices [OK]

Common Mistakes:

• Assuming loop variable is index
• Trying to index string with a character
• Confusing loop variable with range

5. Write code to count how many vowels are in the string sentence. Which code correctly does this?

hard

A. count = 0
for ch in sentence:
if ch in 'aeiouAEIOU':
count += 1
print(count)

B. count = 0
for i in range(len(sentence)):
if sentence[i] == 'aeiou':
count += 1
print(count)

C. count = 0
for ch in sentence:
if ch == 'a' or 'e' or 'i' or 'o' or 'u':
count += 1
print(count)

D. count = 0
for ch in sentence:
if ch in ['a','e','i','o','u']:
count = count + 1
print(count)

Solution

1. Step 1: Check vowel membership correctly

   count = 0 for ch in sentence: if ch in 'aeiouAEIOU': count += 1 print(count) checks if each character is in the string of vowels (both lowercase and uppercase), which is correct.

2. Step 2: Verify counting logic

   count = 0 for ch in sentence: if ch in 'aeiouAEIOU': count += 1 print(count) increments count correctly when a vowel is found and prints the total count.

3. Final Answer:

   count = 0 for ch in sentence: if ch in 'aeiouAEIOU': count += 1 print(count) -> Option A

4. Quick Check:

   Use 'in' with vowel string and increment count [OK]

Hint: Use 'if ch in "aeiouAEIOU"' to check vowels [OK]

Common Mistakes:

• Using '==' to compare with multiple vowels
• Checking membership incorrectly with list without uppercase
• Not incrementing count properly