Data Structure & Function
Cracking String Secrets |
Learning Outcome
5
4
3
2
1
Understand string creation using different quote types
Apply indexing and slicing for string access
Explain immutability and string modification limitations
Use common string methods for text manipulation
Perform string comparison and search operations
What is a String in Python?
Strings are sequences of characters enclosed within quotes.They can contain letters, numbers, symbols, and spaces.
Characters in a string follow a specific sequence.
A string can contain repeated characters.
You can loop through each character in a string.
In Python, strings can be created in two ways...
Using Triple Quotes (Multi-line Strings)
Using Single and Double Quotes
You can create strings using either single quotes (' ') or double quotes (" ").
✔ Both work the same way
✔ Choice depends on convenience
name = 'Rahul'
city = "Mumbai"
Triple quotes (''' ''' or """ """) are used for multi-line strings.
text = """This is a multi-line
string"""
✔ Useful for paragraphs or long text
✔ Preserves formatting (line breaks)
Accessing characters in String
Once you define a string, python allocate an index value for its each character.
These index values are used to access and manipulate the strings.
name = "ITVedant Education"
1
0
3
2
4
5
7
6
8
9
10
11
12
13
14
15
16
17
Accessing characters in String
The positive index 0 is assigned to the first character and n-1 to the last character, where n is the number of characters in the string.
The negative index assigned from the last character to the first character in reverse order begins with -1.
I
T
V
E
D
A
N
T
0
1
2
3
4
5
6
7
-1
-2
-3
-4
-5
-6
-7
-8
Example 1: Access specific characters through positive indexing.
text = "Python"
print(text[0])
print(text[2])
P
t
=== Code Execution Successful ===
Example 2: Read characters from the end using negative indices.
n
h
=== Code Execution Successful ===
text = "Python"
print(text[-1])
print(text[-3])
String Slicing
In Python, string slicing is a technique used to extract a specific portion (substring) of a string by specifying a range of indices.
Because strings are immutable, slicing does not modify the original string; instead, it creates a new one.
s = "Python"
print(s[1:4])
print(s[:3])
print(s[3:])
print(s[::-1])Example: this example demonstrates slicing through range and reversing a string.
yth
Pyt
hon
nohtyP
=== Code Execution Successful ===
String[start:end]
Syntax
Once a String is created, it cannot be modified. Any operation that appears to change a String actually creates a new one.
Understanding String Immutability
For Example: Original String Created
name = "Python"Attempt to Modify
name[0] = "J"
Reassignment Required
Output: TypeError
Output: Jython
name = "J" + name[1:] print(name)
Common String Methods
strip()
strip() removes leading and trailing whitespace from the string
replace()
replace() replaces all occurrences of a specified substring with another.
len()
returns the total number of characters in a string (including spaces and punctuation).
upper()/lower()
upper() converts characters to uppercase, while lower() converts them to lowercase.
Note: These are some of the commonly used string methods; many more are available for you to explore.
text = " Python Programming "
print(len(text))
print(text.upper())
print(text.lower())
print(text.strip())
print(text.replace("Python", "Java"))22
PYTHON PROGRAMMING
python programming
Python Programming
Java Programming
=== Code Execution Successful ===
Concatenating and Repeating Strings
We can concatenate strings using
operator and repeat them using
+
operator.
*
1. Strings can be combined by using + operator.
Example: Join two words with a space.
s1 = "Hello"
s2 = "World"
print(s1 + " " + s2)
Output : Hello World
2. We can repeat a string multiple times using * operator.
Example: Repeat “Hello” three times.
s = "Hello "
print(s * 3)
Output: Hello Hello Hello
String Comparison in Python
Python provides several operators for string comparison, such as ==, !=, <, <=, >, and >=.
These operators are used to check equality as well as perform lexicographical (alphabetical) comparisons.
!= checks if two strings differ.
Let's take a simple example to illustrate these operators.
s1 = "apple"
s2 = "banana"
print(s1 == s2)
print(s1 != s2)
print(s1 < s2)== checks if two strings are identical.
<, <=, >, >= perform lexicographical comparisons based on alphabetical order.
False
True
True
=== Code Execution Successful ===
Locating Text in Strings
Python provides several built-in methods and operators to search for characters or substrings within a string.
find()
Searches for the first occurrence and returns its index. If not found, it returns -1.
index()
Similar to find(), but raises a ValueError if the substring is not found.
startswith()
Returns True if the string begins with the specified prefix.
endswith()
Returns True if the string ends with the specified suffix.
Locating Text in Strings
text = "Python Programming"
# find()
print(text.find("Pro")) # first occurrence
print(text.find("Java")) # not found
# index()
print(text.index("Pro")) # first occurrence
# print(text.index("Java")) # would raise ValueError
# startswith()
print(text.startswith("Python"))
# endswith()
print(text.endswith("ing"))
7
-1
7
True
True
=== Code Execution Successful ===
Summary
5
Comparison and search operations analyze string content
4
Built-in methods simplify string manipulation tasks
3
Indexing and slicing help access string parts
2
Strings are immutable and cannot be modified
1
Strings are sequences of characters within quotes
Quiz
Which of the following statements about Python strings is correct?
A. Strings can be modified after creation
B. Strings are immutable
C. Strings do not support indexing
D. Strings cannot store numbers
Which of the following statements about Python strings is correct?
A. Strings can be modified after creation
B. Strings are immutable
C. Strings do not support indexing
D. Strings cannot store numbers
Quiz-Answer
