str — String Data Type

Visual reference

What you will learn

• Understand str — what a string really is
• Quotes — single, double, and triple quotes
• Sequence — indexing and slicing preview
• Immutability — why characters cannot be changed in place

Chapter 1 — What is a string?

str is a pre-defined class and a sequence data type.

Purpose: store string data, text, alphanumeric data, numeric characters, and special symbols inside single quotes, double quotes, or triple quotes.

Definition: a string is a collection of characters enclosed within quotes. Each character has a position called an index.

Real-world examples

Data	Type
"Mahesh"	str
"DWEL-146"	str
"A+"	str
"admin@example.com"	str
"₹12,500"	str

From your notes: "123456", "Python3.11", "123$456_abc", and "@#$%^&8912" are all str.

Chapter 2 — Why is it called a sequence type?

Sequence means order matters. Think of a beaded necklace — each bead is one character; position is preserved.

• Characters are accessed by index
• The first character is index 0

word = "Python"

print(word[0])
print(word[1])
print(word[5])

P
y
n

Indexing and slicing are covered in depth in the String Handling module; here is a preview only.

Chapter 3 — Three ways to create strings

Your notes list two kinds of string data: single-line and multi-line. Python offers three quotation styles:

Style	Example	Use
Single quotes	'Python'	Short text
Double quotes	"Python"	Same as single quotes
Triple quotes	"""Text""" or '''Text'''	Multi-line paragraphs

s1 = "Python"
s2 = 'Python'

print(s1)
print(s2)

Python
Python

More examples from your notes:

print("A", type("A"))
print("123456", type("123456"))
print("Python3.11", type("Python3.11"))

Chapter 4 — Digits inside quotes are not numbers

Quotes tell Python: treat these digits as symbols, not quantities.

a = 123
b = "123"

print(type(a))
print(type(b))

<class 'int'>
<class 'str'>

Value	Type
123	int
"123"	str
"007"	str
"9876543210"	str

Phone numbers and roll numbers with leading zeros are usually stored as str, not int.

Chapter 5 — Multi-line strings

Single-line "..." and '...' cannot span rows (from your notes):

# address = "Guido Van Rossum
# SyntaxError: unterminated string literal

Use triple quotes for multi-line string data:

address = """John Doe
221B Baker Street
London"""

print(address)

John Doe
221B Baker Street
London

Your notes also use addresses with Guido Van Rossum / Travis Oliphant blocks — same idea. Triple quotes preserve line breaks exactly as written.

Try it in the playground

Edit the address = """...""" block in the starter code: change names and lines, run again, and see multi-line output.

Chapter 6 — Escape characters

Sometimes you need special characters inside strings:

Escape	Meaning
\n	New line
\t	Tab
\"	Double quote inside double-quoted string
\'	Single quote inside single-quoted string
\\	Backslash

print("Hello\nWorld")

Hello
World

print('He said "Hello"')
print("He said \"Hello\"")

Chapter 7 — Strings are immutable

Immutable means you cannot change a character in place after the string is created.

word = "Python"
# word[0] = "J"
# TypeError: 'str' object does not support item assignment

Correct approach: build a new string:

word = "Python"
word = "J" + word[1:]
print(word)

Jython

Chapter 8 — Concatenation vs addition

+ means numeric addition for numbers and concatenation for strings.

print(10 + 20)
print("10" + "20")

30
1020

In the playground, change s = "Python" (add your own text) and use len(s), s[0], and type(s).

Chapter 9 — Preview of indexing and slicing

Every character has a positive index (from 0) and a negative index (from the end).

word = "Python"

print(word[0])
print(word[-1])
print(word[1:4])

P
n
yth

Practice exercises

1. Store your name in a variable and print type(name).
2. Build a three-line address with triple quotes (like your notes’ Guido / Travis examples).
3. Predict "10" + "20" before running the playground.

Quick knowledge check

1. Is "123" an integer?
   No — it is a str.

2. Which quotes allow multi-line strings?
   Triple quotes (""" or ''').

3. What is "10" + "20"?
   "1020" (concatenation), not 30.

Summary

• str is Python’s text type — an ordered sequence of characters.
• Use '...' or "..." for single-line text; """...""" for multi-line.
• Digits in quotes are characters, not numeric types.
• Strings are immutable — create new strings instead of assigning to word[0].
• + concatenates strings; indexing/slicing are previewed here and expanded later.

Next lesson: bytes — immutable byte sequences and the difference between str and bytes.