String slicing behavior in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the first three characters of the string.

Python

text = "hello"
slice = text[[1]]
print(slice)

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

A0:3

B1:4

C3:5

D2:5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1:4 instead of 0:3 to get the first three characters.

Forgetting that the end index is not included in slicing.

To get the first three characters, we slice from index 0 up to (but not including) 3.

2fill in blank

medium

Complete the code to get the last two characters of the string.

Python

text = "world"
slice = text[[1]]
print(slice)

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

A-3:-1

B3:5

C2:4

D-2:

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3:5 works but is less flexible for strings of different lengths.

Using -3:-1 misses the last character.

Using negative indices, -2: means from the second last character to the end.

3fill in blank

hard

Fix the error in the code to reverse the string using slicing.

Python

text = "python"
reversed_text = text[[1]]
print(reversed_text)

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

A::-1

B1::-1

C::-2

D1:0:-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1::-1 only reverses part of the string.

Using ::-2 skips characters and does not fully reverse.

The slice ::-1 reverses the string by stepping backwards one character at a time.

4fill in blank

hard

Fill both blanks to get every second character from index 1 to 6.

Python

text = "abcdefghij"
slice = text[[1]:[2]:2]
print(slice)

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

A1

B6

C5

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1:5 misses the character at index 5.

Using 1:7 includes an extra character beyond index 6.

Start at index 1 and go up to (but not including) index 6, stepping by 2 to get every second character.

5fill in blank

hard

Fill all three blanks to extract characters from index 2 to 8 skipping every 3rd character.

Python

text = "abcdefghijklm"
slice = text[[1]:[2]:[3]]
print(slice)

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

A2

B8

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using step 5 skips too many characters.

Using stop index 5 cuts the slice too short.

Start at index 2, go up to (not including) 8, stepping by 3 to skip every 3rd character.

Practice

1. What does the slice s[2:5] do on the string s = 'Python'?

easy

A. Extracts characters from index 5 to index 2

B. Extracts characters from index 2 to index 5 including both

C. Extracts characters from the start to index 5

D. Extracts characters from index 2 up to but not including index 5

Solution

1. Step 1: Understand slice notation s[start:stop]

   The slice includes the start index but excludes the stop index.

2. Step 2: Apply to s = 'Python' with s[2:5]

   Characters at indices 2, 3, 4 are 't', 'h', 'o'. Index 5 is excluded.

3. Final Answer:

   Extracts characters from index 2 up to but not including index 5 -> Option D

4. Quick Check:

   Slice excludes stop index [OK]

Hint: Remember stop index is excluded in slicing [OK]

Common Mistakes:

• Including the stop index character
• Confusing start and stop positions
• Thinking slicing reverses string by default

2. Which of the following is the correct syntax to get every second character from string s starting from the first character?

easy

A. s[:2:2]

B. s[2::]

C. s[::2]

D. s[1:2]

Solution

1. Step 1: Understand slice syntax s[start:stop:step]

   The step value controls the interval between characters taken.

2. Step 2: Identify correct syntax for every second character from start

   s[::2] means start at 0, go to end, step by 2, so every second character.

3. Final Answer:

   s[::2] -> Option C

4. Quick Check:

   Step controls interval [OK]

Hint: Use empty start and stop with step for intervals [OK]

Common Mistakes:

• Using wrong start index
• Confusing step with stop
• Using slice with only two colons incorrectly

3. What is the output of the following code?

s = 'abcdefg'
print(s[5:2:-1])

medium

A. 'cde'

B. 'fed'

C. 'edc'

D. 'gfed'

Solution

1. Step 1: Understand slicing with negative step

   Negative step means slicing backwards. Start at index 5, stop before index 2.

2. Step 2: Extract characters from s = 'abcdefg'

   Index 5 is 'f', then 'e' at 4, then 'd' at 3. Stop before 2 means exclude index 2 ('c'). So result is 'fed'.

3. Final Answer:

   'fed' -> Option B

4. Quick Check:

   Negative step slices backwards excluding stop [OK]

Hint: Negative step slices backward excluding stop index [OK]

Common Mistakes:

• Including stop index when stepping backwards
• Confusing forward and backward slicing
• Misreading indices for negative step

4. Find the error in this code snippet:

s = 'hello'
print(s[4:1])

medium

A. No error, prints empty string

B. No error, prints 'llo'

C. SyntaxError due to invalid slice

D. RuntimeError due to wrong indices

Solution

1. Step 1: Analyze slice s[4:1]

   Start index 4, stop index 1, default step is +1, so slice moves forward.

2. Step 2: Understand slice behavior when start > stop with positive step

   Since start is after stop and step is positive, slice returns empty string without error.

3. Final Answer:

   No error, prints empty string -> Option A

4. Quick Check:

   Forward slice with start > stop = empty string [OK]

Hint: Forward slice with start > stop returns empty string [OK]

Common Mistakes:

• Expecting an error for invalid slice
• Expecting reversed substring without negative step
• Confusing slice indices order

5. Given s = 'abcdefgh', which slice extracts the string 'hgfed'?

hard

A. s[7:2:-1]

B. s[7:3:-1]

C. s[7:1:-1]

D. s[7:0:-1]

Solution

1. Step 1: Identify characters in 'hgfed'

   These are characters at indices 7 ('h'), 6 ('g'), 5 ('f'), 4 ('e'), 3 ('d').

2. Step 2: Check slice s[7:2:-1]

   Start at index 7 ('h'), move backward to index 3 (stop before 2), so includes indices 7 to 3. This matches 'hgfed'.

3. Final Answer:

   s[7:2:-1] -> Option A

4. Quick Check:

   Negative step excludes stop index [OK]

Hint: Negative step excludes stop index, count backward carefully [OK]

Common Mistakes:

• Including stop index in negative step slice
• Choosing wrong stop index
• Confusing slice direction with step sign