UNIT-2: Python Strings and Operators
Python Strings
A string in Python is a sequence of characters enclosed in single (‘ ‘), double (” “), or triple quotes (”’ ”’ or “”” “””).
Strings are immutable, meaning they cannot be changed after creation.
Python provides various ways to manipulate and work with strings efficiently.
Multiline String, String as Character Array, Triple Quotes
1. Multiline Strings
Python allows storing multiple lines in a string using triple quotes (''' or """).
Example:
multi_line = """This is a multi-line string in Python.""" print(multi_line)
OUTPUT :-
This is a multi-line string in Python.
2. String as a Character Array.
In Python, strings are sequences of characters and can be accessed like an array (list) using indexing.
Example:
text = "Python" print(text[0]) # Output: P (First character) print(text[3]) # Output: h
Strings are immutable: You cannot modify a string after creation, but you can reassign it
text[0] = "J" # ❌ Error: Strings are immutable
3. Triple Quotes (''' or """).
Triple quotes (''' or """) are used for multiline strings and docstrings (function documentation).
Example:
def sample_function():
"""This function demonstrates docstrings in Python."""
return "Hello"
print(sample_function.__doc__) # Output: This function demonstrates docstrings in Python.
✅ Use Cases:
Multiline strings
Function documentation (docstrings)
Slicing Strings, Negative Indexing, String Length, Concatenation
1. Slicing Strings
String slicing extracts a substring using [start:end:step] notation.
Syntax:
substring = string[start:end] # End index is exclusive
EXAMPLE
text = "Python Programming" print(text[0:6]) # Output: Python print(text[7:18]) # Output: Programming print(text[:6]) # Output: Python (Start from 0) print(text[7:]) # Output: Programming (Till end) print(text[::2]) # Output: Pto rgamn (Every second character)
2. Negative Indexing
Python allows negative indexing to access characters from the end.
text = "Python" print(text[-1]) # Output: n (Last character) print(text[-3:]) # Output: hon (Last three characters) print(text[:-2]) # Output: Pyth (Excludes last two characters)
✅ Benefits:
Easy access to the last characters without knowing string length.
3. Finding String Length
The len() function returns the number of characters in a string.
text = "Hello, Python!" print(len(text)) # Output: 14
4. String Concatenation
Concatenation joins two or more strings using the + operator.
Example:
text1 = "Hello" text2 = "World" result = text1 + " " + text2 # Adding space between words print(result) # Output: Hello World
✅ Alternative: Using join() method
words = ["Hello", "World"] result = " ".join(words) print(result) # Output: Hello World
String Methods.
| Method | Description | Example |
|---|---|---|
| center(width) | Centers the string within a given width | "Python".center(10) → ' Python ' |
| count(substring) | Counts occurrences of a substring | "banana".count("a") → 3 |
| join(iterable) | Joins elements of an iterable with a separator | "-".join(["A", "B", "C"]) → "A-B-C" |
| len(string) | Returns the length of a string | len("Python") → 6 |
| max(string) | Returns the highest character (ASCII-wise) | max("hello") → 'o' |
| min(string) | Returns the lowest character (ASCII-wise) | min("hello") → 'e' |
| replace(old, new) | Replaces occurrences of a substring | "hello".replace("l", "x") → "hexxo" |
| lower() | Converts to lowercase | "Python".lower() → "python" |
| upper() | Converts to uppercase | "python".upper() → "PYTHON" |
| split(separator) | Splits a string into a list | "hello world".split(" ") → ['hello', 'world'] |
Examples of String Methods
1. center() Method
text = "Python" print(text.center(10)) # Output: ' Python '
2. count() Method
text = "banana"
print(text.count("a")) # Output: 3
3. join() Method
words = ["Python", "is", "fun"] result = " ".join(words) print(result) # Output: Python is fun
4. replace() Method
text = "Hello World"
new_text = text.replace("World", "Python")
print(new_text) # Output: Hello Python
5. upper() and lower() Methods
text = "Python" print(text.upper()) # Output: PYTHON print(text.lower()) # Output: python
6. split() Method.
text = "apple,banana,cherry"
words = text.split(",")
print(words) # Output: ['apple', 'banana', 'cherry']
Operators in Python.
Operators in Python are symbols that perform operations on variables and values.
Python supports different types of operators, such as arithmetic, assignment, comparison, logical, identity, and membership operators.
Arithmetic Operators.
Arithmetic operators perform mathematical operations like addition, subtraction, multiplication, division, etc..
| Operator | Description | Example |
|---|---|---|
| + | Addition | 5 + 3 → 8 |
| - | Subtraction | 10 - 4 → 6 |
| * | Multiplication | 6 * 2 → 12 |
| / | Division (returns float) | 9 / 2 → 4.5 |
| // | Floor Division (rounds down) | 9 // 2 → 4 |
| % | Modulus (remainder) | 9 % 2 → 1 |
| ** | Exponentiation (power) | 2 ** 3 → 8 |
a = 10 b = 3 print(a + b) # 13 print(a - b) # 7 print(a * b) # 30 print(a / b) # 3.3333 print(a % b) # 1 print(a ** b) # 1000 (10^3) print(a // b) # 3 (Rounded down)
Assignment Operators
Assignment operators are used to assign values to variables.
| Operator | Example | Equivalent To |
|---|---|---|
| = | a = 5 | Assigns 5 to a |
| += | a += 3 | a = a + 3 |
| -= | a -= 2 | a = a - 2 |
| *= | a *= 4 | a = a * 4 |
| /= | a /= 2 | a= a / 2 |
| //= | a //= 2 | a = a // 2 |
| %= | a %= 3 | a = a % 3 |
| **= | a **= 2 | a = a ** 2 |
x = 10 x += 5 # x = x + 5 print(x) # Output: 15 x *= 2 # x = x * 2 print(x) # Output: 30 x //= 3 # x = x // 3 print(x) # Output: 10
Comparison Operators.
Comparison operators compare two values and return True or False.
| Operator | Description | Example |
|---|---|---|
| == | Equal to | 5 == 5 → True |
| != | Not equal to | 5 != 3 → True |
| > | Greater than | 10 > 3 → True |
| < | Less than | 2 < 5 → True |
| >= | Greater than or equal to | 10 >= 10 → True |
| <= | Less than or equal to | 5 <= 6 → True |
a = 10 b = 20 print(a == b) # False print(a != b) # True print(a > b) # False print(a < b) # True print(a >= 10) # True print(b <= 10) # False
Logical Operators.
Logical operators are used to combine conditional statements.
| Operator | Description | Example |
|---|---|---|
| and | Returns True if both conditions are True | (5 > 3 and 10 > 5) → True |
| or | Returns True if at least one condition is True | (5 > 3 or 10 < 5) → True |
| not | Reverses the condition | not(5 > 3) → False |
x = 5
y = 10
print(x > 2 and y > 5) # True (Both conditions are True)
print(x > 10 or y > 5) # True (One condition is True)
print(not (x > 2)) # False (Reverses the condition)
Identity and Membership Operators.
1. Identity Operators (is, is not)
Identity operators check if two variables refer to the same memory location.
| Operator | Description | Example |
|---|---|---|
| is | Returns True if two variables refer to the same object | a is b | is not | Returns True if two variables refer to different objects | a is not b |
| Operator | Description | Example |
|---|---|---|
| in | Returns True if a value is in a sequence | "a" in "apple" → True |
| not in | Returns True if a value is not in a sequence | "z" not in "apple" → True |
text = "Python Programming"
print("Python" in text) # True
print("Java" in text) # False
print("Java" not in text) # True
Conclusion.
Python strings are sequences of characters that support slicing, indexing, and modification using built-in methods.
Multiline strings use triple quotes.
Slicing and negative indexing help extract substrings easily.
String methods like
replace(),join(), andsplit()make string operations more efficient.Arithmetic operators perform mathematical operations.
Assignment operators update variable values.
Comparison operators compare values and return
True/False.Logical operators combine conditions.
Identity operators check object identity in memory.
Membership operators check if an element is in a sequence.
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