How Strings Work Differently Across Languages in DSA Python - Code Step by Step

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the first character of the string.

DSA Python

first_char = my_string[[1]]

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

A1

B0

C-1

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first index

Using negative indices incorrectly

In Python, string indexing starts at 0, so the first character is at index 0.

2fill in blank

medium

Complete the code to get the substring from index 2 to 5 (exclusive).

DSA Python

substring = my_string[[1]]

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

A2..5

B2,5

C2:5

D2-5

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas or dashes instead of colon

Including the end index character

Python uses slice notation with a colon to get substrings: start index inclusive, end index exclusive.

3fill in blank

hard

Fix the error in the code to concatenate two strings correctly.

DSA Python

full_string = str1 [1] str2

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

A/

B*

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' which repeats strings

Using arithmetic operators like '-' or '/'

In Python, the '+' operator concatenates strings.

4fill in blank

hard

Complete the code to create a dictionary with words as keys and their lengths as values, only for words longer than 3 characters.

DSA Python

lengths = {word: [1] for word in words if len(word) > 3}

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

Blen(word)

Cword

Dword.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Adding extra characters after word for key

Using word instead of len(word) for value

The key is the word itself (no extra syntax), and the value is the length of the word using len(word).

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys and their lengths as values, only for words shorter than 5 characters.

DSA Python

result = { [1]: [2] for word in words if len(word) [3] 5}

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

Aword.upper()

Blen(word)

C<

Dword.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.lower() instead of upper()

Using > instead of < in condition

Keys are uppercase words using word.upper(), values are lengths with len(word), and the condition checks words shorter than 5 using <.

Practice

1. In Python, what is the type of a string like "hello"?

easy

A. A mutable list of characters

B. An immutable sequence of characters

C. A fixed-size array of bytes

D. A pointer to a memory address

Solution

1. Step 1: Understand Python string type

   Python strings are sequences of characters that cannot be changed after creation.

2. Step 2: Compare with options

   An immutable sequence of characters correctly describes strings as immutable sequences. Options A, C, and D do not match Python's string behavior.

3. Final Answer:

   An immutable sequence of characters -> Option B

4. Quick Check:

   Python strings are immutable sequences [OK]

Hint: Remember: Python strings cannot be changed after creation [OK]

Common Mistakes:

• Thinking strings are mutable like lists
• Confusing strings with byte arrays
• Assuming strings are pointers

2. Which of the following is the correct way to create a multi-line string in Python?

easy

A. Using triple quotes like '''Hello\nWorld'''

B. Using backslash at end of each line like 'Hello\n\World'

C. Using double quotes only like "Hello\nWorld"

D. Using parentheses without quotes like (Hello\nWorld)

Solution

1. Step 1: Identify Python multi-line string syntax

   Python uses triple quotes (''' or """) to create multi-line strings easily.

2. Step 2: Check options

   Using triple quotes like '''Hello\nWorld''' uses triple quotes correctly. Using backslash at end of each line like 'Hello\n\World' is invalid syntax. Using double quotes only like "Hello\nWorld" creates a single-line string with \n as newline character but not multi-line. Using parentheses without quotes like (Hello\nWorld) is invalid syntax.

3. Final Answer:

   Using triple quotes like '''Hello\nWorld''' -> Option A

4. Quick Check:

   Triple quotes create multi-line strings [OK]

Hint: Use triple quotes for multi-line strings in Python [OK]

Common Mistakes:

• Using backslash incorrectly for multi-line
• Confusing escape sequences with multi-line strings
• Omitting quotes around strings

3. What is the output of this Python code?

text = 'abc'
text[1] = 'z'
print(text)

medium

A. IndexError

B. abc

C. abz

D. TypeError

Solution

1. Step 1: Understand string immutability in Python

   Strings cannot be changed by assigning to an index; this causes an error.

2. Step 2: Identify error type

   Assigning to text[1] causes a TypeError: 'str' object does not support item assignment.

3. Final Answer:

   TypeError -> Option D

4. Quick Check:

   Strings are immutable, so assignment causes TypeError [OK]

Hint: Strings cannot be changed by index assignment in Python [OK]

Common Mistakes:

• Expecting string to change like a list
• Confusing TypeError with IndexError
• Ignoring immutability of strings

4. Find the error in this Python code snippet:

my_str = "hello"
my_str[0] = 'H'
print(my_str)

medium

A. TypeError because strings are immutable

B. SyntaxError due to quotes

C. No error, output is 'Hello'

D. NameError due to undefined variable

Solution

1. Step 1: Check string modification attempt

   The code tries to change the first character of a string, which is not allowed.

2. Step 2: Identify error type

   This causes a TypeError because strings in Python cannot be changed after creation.

3. Final Answer:

   TypeError because strings are immutable -> Option A

4. Quick Check:

   Strings are immutable, so assignment causes TypeError [OK]

Hint: Strings cannot be changed by index assignment in Python [OK]

Common Mistakes:

• Thinking strings behave like lists
• Expecting output 'Hello' without error
• Confusing error types

5. Given the list words = ['apple', 'banana', 'cherry'], which Python code correctly creates a new list with the first letter of each word capitalized, considering strings are immutable?

hard

A. words.map(lambda w: w.capitalize())

B. for word in words: word[0] = word[0].upper()

C. [word[0].upper() + word[1:] for word in words]

D. words = words.upper()

Solution

1. Step 1: Understand string immutability and list comprehension

   Since strings cannot be changed, create new strings with capitalized first letters using list comprehension.

2. Step 2: Analyze options

   [word[0].upper() + word[1:] for word in words] correctly creates new strings by combining uppercase first letter and rest of string. for word in words: word[0] = word[0].upper() tries to assign to string index, causing error. words.map(lambda w: w.capitalize()) uses invalid syntax in Python. words = words.upper() tries to call upper() on list, which is invalid.

3. Final Answer:

   [word[0].upper() + word[1:] for word in words] -> Option C

4. Quick Check:

   Use list comprehension with new strings to handle immutability [OK]

Hint: Use list comprehension to create new strings, not modify in place [OK]

Common Mistakes:

• Trying to assign to string characters
• Using invalid methods on lists
• Confusing Python with other languages' syntax