PART 2 • LEVEL 06

🔤 Strings

Create, inspect, transform and analyse text using precise indexing, slicing, methods, formatting and traversal techniques.

⏱ 90–105 minutes📚 8 concepts💻 5 programs🧠 6-question quiz

Start Lesson ↓Jump to Problems

student_name.pyPython 3

raw_name = "  code bhavya  "
clean_name = raw_name.strip().title()
first_word = clean_name[:4]

print(f"Name: {clean_name}")
print(f"Prefix: {first_word}")
print(f"Length: {len(clean_name)}")

OUTPUTName: Code Bhavya
Prefix: Code
Length: 11

LEARNING OUTCOMES

By the End of This Level

You will be able to process text safely and clearly.

Create strings and explain their immutable nature.

Access characters using positive and negative indexes.

Extract and reverse text using slicing.

Transform, search, format and traverse strings.

TEXT VALUES

String Fundamentals and Immutability

A string is an ordered sequence of Unicode characters written inside matching quotes.

Single quotes, double quotes and triple quotes can create strings. Choose quotes that keep the content readable; triple quotes are useful for multi-line text.

Immutable

A string cannot be changed in place. Every apparent modification creates and returns a new string value.

Single quotes'Python'

Double quotes"CodeBhavya"

Empty string""

Lengthlen("Python") → 6

Immutability rule

word[0] = "J" raises an error. Build a new value instead, such as "J" + word[1:].

ONE CHARACTER

String Indexing

Indexing retrieves one character. Positive indexes begin at the left with 0; negative indexes begin at the right with −1.

Expression	Position	Result for `"Python"`
`word[0]`	First character	`'P'`
`word[2]`	Third character	`'t'`
`word[-1]`	Last character	`'n'`
`word[-2]`	Second from the end	`'o'`

EXAMPLE 1

Inspect Boundary Characters

course = "Python"
print("First:", course[0])
print("Last:", course[-1])

OUTPUT

First: P
Last: n

SUBSTRING

String Slicing

Slicing uses text[start:stop:step]. The start is included and the stop is excluded.

1Choose StartIncluded index

→

2Choose StopExcluded index

→

3Choose StepMovement amount

→

4Build ResultNew string

Slice	Meaning	Result for `"CodeBhavya"`
`text[0:4]`	Indexes 0 through 3	`Code`
`text[4:]`	Index 4 to the end	`Bhavya`
`text[:4]`	Beginning through index 3	`Code`
`text[::2]`	Every second character	`CdBaya`
`text[::-1]`	Reverse the sequence	`ayvahBedoC`

COMBINE AND TEST

String Operators and Membership

➕

Concatenation

"Code" + "Bhavya" joins strings.

✖️

Repetition

"ha" * 3 produces hahaha.

🔍

Membership

"Py" in "Python" is True.

⚖️

Comparison

Strings compare character by character using Unicode order.

EXAMPLE 2

Build and Search Text

brand = "Code" + "Bhavya"
has_code = "Code" in brand
print(brand)
print("Contains Code:", has_code)

OUTPUT

CodeBhavya
Contains Code: True

TRANSFORM AND SEARCH

Essential String Methods

Method	Purpose	Example result
`strip()`	Remove outer whitespace	`" hi ".strip()` → `"hi"`
`lower()` / `upper()`	Change letter case	`"Py".lower()` → `"py"`
`title()`	Capitalize words	`"code bhavya".title()`
`replace()`	Replace occurrences	`"2025".replace("5", "6")`
`find()`	Return first index or −1	`"Python".find("th")` → `2`
`count()`	Count occurrences	`"banana".count("a")` → `3`
`startswith()`	Test the beginning	`"Python".startswith("Py")`
`isalpha()`	Test letters only	`"Code".isalpha()`

Methods return values

Because strings are immutable, write clean = raw.strip(). Calling raw.strip() alone does not alter raw.

CLEAR OUTPUT

String Formatting

F-strings place expressions directly inside braces and are the clearest general choice for modern Python formatting.

EXAMPLE 3

Student Summary

name = "Bhavya"
score = 92.456
print(f"{name} scored {score:.2f}")

OUTPUT

Bhavya scored 92.46

RECOMMENDED

F-string

f"Name: {name}"

Readable and supports expressions.

METHOD

`format()`

"Name: {}".format(name)

Useful in older code and templates.

SIMPLE

Comma printing

print("Name:", name)

Convenient for basic labelled output.

CHARACTER BY CHARACTER

String Traversal and Counting

A for loop can visit each character directly, making classification and counting problems easy to express.

EXAMPLE 4

Count Vowels

text = "Education"
vowels = 0

for character in text.lower():
    if character in "aeiou":
        vowels += 1

print("Vowels =", vowels)

OUTPUT

Vowels = 5

DEBUGGING CORNER

Common String Mistakes

Index Range

word[10]

An unavailable index raises IndexError; valid positive indexes stop at len(word) - 1.

Slice Stop

word[1:4]

The character at index 4 is excluded.

Immutability

word[0] = "J"

Create a new string instead of assigning to one character.

Method Result

name.strip()

Store or use the returned string; the original value remains unchanged.

Debug text processing:1. Display repr() when spaces matter2. Check length3. Mark indexes4. Verify slice boundaries5. Store method results

QUICK REVISION

📌 Strings — Quick Revision

Review these rules before attempting the quiz and programming problems.

A string is an ordered, immutable character sequence.

Positive indexing starts at 0.

Negative indexing starts at −1 from the right.

A slice excludes its stop index.

[::-1] reverses a string.

+ joins strings and * repeats them.

in and not in test membership.

String methods return new values.

F-strings combine text and expressions clearly.

A for loop can visit every character directly.

KNOWLEDGE CHECK

Level 6 Quick Quiz

Select one answer for every question, then check your score.

6 Questions

1What is "Python"[-1]?PnoError

2What is "Python"[1:4]?Pytythoyththo

3Which expression reverses text?text[::-1]text[1:]text[-1]text.reverse()

4What does strip() remove by default?Every internal spaceOnly newline charactersAll punctuationLeading and trailing whitespace

5Which statement about strings is correct?Characters can always be assigned directlyStrings are immutableIndexes begin at 1len() excludes spaces

6What is "banana".count("a")?1234

PRACTICE

🎯 5 Programming Problems — Strings

Follow the CodeBhavya pattern: understand the task, inspect the sample, use the editor, run, check, then compare with the official program.

📈 Strings Practice Progress

Solved0 / 5

Completed with Solution0

Total Score0 / 500

Completion0%

A problem counts as Solved when its output passes before the official solution is opened.

1. Clean Student Name

Remove outer spaces and convert the supplied name to title case.

Sample input: code bhavya Expected output: Clean = Code Bhavya

💡 Chain strip() and title().

Official Python Program

name = input()
clean = name.strip().title()
print("Clean =", clean)

2. Character at an Index

Read text and an index, then display the character at that index.

Sample input: Python, 2Expected output: Character = t

Official Python Program

text = input()
index = int(input())
character = text[index]
print("Character =", character)

3. Extract the Brand Name

Read text, start and stop indexes, then display the requested slice.

Sample input: CodeBhavya, 4, 10Expected output: Slice = Bhavya

💡 Use text[start:stop]; the stop index is excluded.

Official Python Program

text = input()
start = int(input())
stop = int(input())
part = text[start:stop]
print("Slice =", part)

4. Reverse Text

Read a string and display it in reverse order using slicing.

Sample input: CodeBhavyaExpected output: Reversed = ayvahBedoC

💡 A slice with step -1 visits characters from right to left.

Official Python Program

text = input()
reversed_text = text[::-1]
print("Reversed =", reversed_text)

5. Count Vowels

Read text and count its vowels without treating uppercase and lowercase differently.

Sample input: EducationExpected output: Vowels = 5

💡 Convert the text to lowercase, traverse it and test membership in "aeiou".

Official Python Program

text = input()
vowels = 0
for character in text.lower():
    if character in "aeiou":
        vowels += 1
print("Vowels =", vowels)

KEY TAKEAWAY

🎯 Treat Text as an Ordered Sequence

1Normalize

Clean spaces and letter case.

→

2Locate

Use indexes and slices precisely.

→

3Transform

Store method results as new strings.

→

4Analyse

Traverse and count characters.

Reliable text processing starts by understanding that strings are ordered and immutable: inspect precisely, transform into new values and verify boundaries.

INTERACTIVE LEARNING

🎬 String Slicing — Visual Flow

Watch Python evaluate "Python"[1:5:2] from its start, stop and step values.

PROGRAM TRACING

🔎 Program Tracing — Vowel Counter

Trace each character in Code and observe how the vowel counter changes.

INTERVIEW PREPARATION

🎤 Strings — Interview Questions

Answer aloud before opening each explanation.

Why are Python strings called immutable?

What is the difference between indexing and slicing?

Indexing retrieves one character and may raise IndexError. Slicing produces a new substring and safely clips out-of-range boundaries.

Why is the stop index excluded from a slice?

The half-open design makes slice length predictable as stop - start when the step is 1 and makes adjacent slices fit without overlap.

What does find() return when text is absent?

find() returns -1. By contrast, index() raises ValueError when the substring is absent.

How do isalpha() and isalnum() differ?

isalpha() requires letters only. isalnum() accepts letters and digits, with at least one character present.

What is the time complexity of scanning every character once?

For a string of length n, a single full traversal takes linear time: O(n).

EXTRA TIPS

💡 Strings — Extra Tips

01
Normalize user input with strip() before validation or comparison.
02
Use casefold() for robust case-insensitive international text comparison.
03
Prefer in when you only need to know whether a substring exists.
04
Use join() for efficiently combining many string pieces.
05
Remember that a space is a character and contributes to len().
06
When debugging hidden whitespace, inspect the value with repr().

EXTRA PRACTICE

✍️ Strings — Extra Practice Questions

Check whether a supplied word is a palindrome.
Count uppercase letters, lowercase letters, digits and spaces separately.
Remove every space from a sentence without using replace().
Find the first and last positions of a supplied character.
Count how many times each vowel occurs.
Replace repeated spaces with a single space.
Display every word of a sentence on a separate line.
Create initials from a full name.
Check whether two strings are anagrams after normalizing case and spaces.
Perform run-length encoding for consecutive repeated characters.

LEVEL 6 CHECKPOINT

Strings Complete

When you can trace indexes, design slices, select suitable methods and solve all five programs without help, mark this level complete and continue.

Continue to Level 7 →

🔤 Strings

By the End of This Level

String Fundamentals and Immutability

String Indexing

Inspect Boundary Characters

String Slicing

String Operators and Membership

Concatenation

Repetition

Membership

Comparison

Build and Search Text

Essential String Methods

String Formatting

Student Summary

F-string

format()

Comma printing

String Traversal and Counting

Count Vowels

Common String Mistakes

📌 Strings — Quick Revision

Level 6 Quick Quiz

🎯 5 Programming Problems — Strings

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

🎯 Treat Text as an Ordered Sequence

🎬 String Slicing — Visual Flow

✂️ How Python Builds a String Slice

1. Read the Indexed Sequence

🔎 Program Tracing — Vowel Counter

🎤 Strings — Interview Questions

💡 Strings — Extra Tips

✍️ Strings — Extra Practice Questions

Strings Complete

`format()`