Python String Methods (Part 2)

Python provides several built-in string methods for checking the properties of strings. These methods help programmers validate user input, compare text, and process strings efficiently.

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Learning Objectives

• Use methods to check string properties.
• Validate user input.
• Understand Boolean return values.
• Apply string methods in real-life programs.

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1. startswith() Method

The startswith() method checks whether a string begins with a specified character or substring. It returns True if the string starts with the given value; otherwise, it returns False.

Syntax

string.startswith(substring)

Example 1

text="Computer Science"
print(text.startswith("Computer"))

Output

True

Example 2

text="Computer Science"
print(text.startswith("Science"))

Output

False

Real-Life Applications

• Checking file extensions.
• Validating URLs.
• Checking prefixes in product codes.
• Filtering records.

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2. endswith() Method

The endswith() method checks whether a string ends with a specified character or substring.

Syntax

string.endswith(substring)

Example 1

filename="notes.pdf"
print(filename.endswith(".pdf"))

Output

True

Example 2

filename="notes.pdf"
print(filename.endswith(".docx"))

Output

False

Real-Life Applications

• Checking image files.
• Validating document formats.
• Checking email domains.
• Filtering uploaded files.

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3. isalnum() Method

The isalnum() method returns True if all characters in the string are alphabetic or numeric. Spaces and special characters are not allowed.

Syntax

string.isalnum()

Example 1

text="ABC123"
print(text.isalnum())

Output

True

Example 2

text="ABC 123"
print(text.isalnum())

Output

False

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4. isalpha() Method

The isalpha() method returns True if all characters in the string are alphabetic.

Syntax

string.isalpha()

Example 1

name="Python"
print(name.isalpha())

Output

True

Example 2

name="Python3"
print(name.isalpha())

Output

False

Applications

• Name validation.
• Checking alphabet-only fields.
• Form validation.

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5. isdigit() Method

The isdigit() method returns True if all characters in the string are digits.

Syntax

string.isdigit()

Example 1

roll="1256"
print(roll.isdigit())

Output

True

Example 2

roll="12A6"
print(roll.isdigit())

Output

False

Applications

• Mobile number validation.
• PIN verification.
• Checking numeric input.

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6. islower() Method

The islower() method returns True if all alphabetic characters in the string are lowercase.

Syntax

string.islower()

Example

text="python"
print(text.islower())

Output

True

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7. isupper() Method

The isupper() method returns True if all alphabetic characters are uppercase.

Syntax

string.isupper()

Example

text="PYTHON"
print(text.isupper())

Output

True

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8. isspace() Method

The isspace() method returns True if the string contains only whitespace characters such as spaces or tabs.

Syntax

string.isspace()

Example 1

text="   "
print(text.isspace())

Output

True

Example 2

text=" Python "
print(text.isspace())

Output

False

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Summary Table

Method	Purpose	Return Type
startswith()	Checks starting text	Boolean
endswith()	Checks ending text	Boolean
isalnum()	Checks letters and digits	Boolean
isalpha()	Checks only alphabets	Boolean
isdigit()	Checks only digits	Boolean
islower()	Checks lowercase letters	Boolean
isupper()	Checks uppercase letters	Boolean
isspace()	Checks whitespace characters	Boolean

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Python String Methods (Part 3)

Python provides several powerful string methods for removing unwanted spaces, replacing text, joining strings, splitting strings, and dividing strings into parts. These methods are widely used in text processing, data cleaning, report generation, and file handling.

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Learning Objectives

• Remove unwanted spaces from strings.
• Replace characters or words.
• Join multiple strings into one.
• Split strings into smaller parts.
• Partition strings using separators.

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1. lstrip() Method

The lstrip() method removes all leading (left-side) whitespace characters from a string.

Syntax

string.lstrip()

Example

text="   Python"
print(text.lstrip())

Output

Python

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2. rstrip() Method

The rstrip() method removes all trailing (right-side) whitespace characters from a string.

Syntax

string.rstrip()

Example

text="Python   "
print(text.rstrip())

Output

Python

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3. strip() Method

The strip() method removes whitespace characters from both the beginning and the end of a string.

Syntax

string.strip()

Example

text="   Python Programming   "
print(text.strip())

Output

Python Programming

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Difference between lstrip(), rstrip() and strip()

Method	Removes Spaces From
lstrip()	Left side only
rstrip()	Right side only
strip()	Both sides

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4. replace() Method

The replace() method replaces all occurrences of a specified substring with another substring.

Syntax

string.replace(old,new)

Example 1

text="I like Java"
print(text.replace("Java","Python"))

Output

I like Python

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Example 2

text="banana"
print(text.replace("a","@"))

Output

b@n@n@

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Real-Life Applications

• Correcting spelling mistakes.
• Replacing old product names.
• Updating records.
• Formatting reports.

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5. join() Method

The join() method joins the elements of a sequence using a specified separator.

Syntax

separator.join(sequence)

Example 1

words=["Python","is","Easy"]
print(" ".join(words))

Output

Python is Easy

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Example 2

letters=["A","B","C","D"]
print("-".join(letters))

Output

A-B-C-D

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6. partition() Method

The partition() method divides a string into three parts based on the first occurrence of a specified separator.

Syntax

string.partition(separator)

Example

text="Computer-Science"
print(text.partition("-"))

Output

('Computer', '-', 'Science')

Explanation: The output is a tuple containing the part before the separator, the separator itself, and the remaining part.

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7. split() Method

The split() method divides a string into a list using the specified separator. If no separator is provided, it splits the string using whitespace.

Syntax

string.split(separator)

Example 1

text="Python Programming Language"
print(text.split())

Output

['Python', 'Programming', 'Language']

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Example 2

text="A,B,C,D"
print(text.split(","))

Output

['A', 'B', 'C', 'D']

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Difference between split() and partition()

split()	partition()
Returns a list.	Returns a tuple.
Splits all occurrences.	Splits only at the first occurrence.
Separator is not included.	Separator is included in the result.

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Summary Table

Method	Purpose
lstrip()	Removes left spaces.
rstrip()	Removes right spaces.
strip()	Removes spaces from both sides.
replace()	Replaces text.
join()	Joins sequence elements.
partition()	Splits into three parts.
split()	Splits into a list.

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Common Programming Mistakes

• Confusing split() with partition().
• Using join() on non-string elements.
• Expecting strip() to remove spaces inside a string.
• Assuming replace() modifies the original string.
• Forgetting that strings are immutable.

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CBSE Important Programs

1. Remove leading and trailing spaces.
2. Replace a word in a sentence.
3. Split a sentence into words.
4. Join a list of names into a sentence.
5. Count the total number of words.
6. Extract the username from an email ID.
7. Split a CSV record.
8. Partition a filename using ".".
9. Replace spaces with underscores.
10. Clean user input before processing.

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Viva Questions

1. Differentiate between strip(), lstrip(), and rstrip().
2. What is the purpose of replace()?
3. How does join() work?
4. What is returned by split()?
5. What is returned by partition()?
6. Differentiate between split() and partition().
7. Does replace() modify the original string?
8. Why are strings called immutable?
9. Give two applications of split().
10. Give two applications of replace().

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Exam Tips

• Remember that strings are immutable.
• split() returns a list.
• partition() returns a tuple.
• join() joins sequence elements using a separator.
• replace() returns a new string.
• strip() removes spaces only from the beginning and end of a string.

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