Q.(A) Write the Python statement for each of the following tasks using built-in functions/methods only:

String Functions: A First Look

Think of a string as a piece of text — a word, a sentence, a name, or even a single character. In computing, strings are everywhere: your name in a form, a product code in a database, a tweet, a paragraph in a document. String functions are the tools that let you work with that text: cut it, join it, clean it, search inside it, or change its appearance.

You already use these ideas in everyday life. When you take a long sentence and pick out just the first word, you are performing a "substring" operation. When you combine your first name and last name into a full name, you are "concatenating" two strings. When you check whether an email address contains an "@" symbol, you are "searching" within a string. String functions are just these familiar actions, given precise names and made available in software.

The Core Idea

A string function takes one or more strings as input and returns a new string or a piece of information about the string. The function does not change the original string — it produces a result based on it. This is important: the original data stays untouched unless you explicitly replace it.

Common Types of String Functions

1. Changing Case

These functions convert text to uppercase or lowercase. They are useful when you want to compare names or addresses without worrying about whether someone typed "Delhi" or "delhi".

• UPPER or UCASE: converts all letters to capitals
• LOWER or LCASE: converts all letters to small letters
• PROPER or TITLE: capitalises the first letter of each word

2. Extracting Parts of a String

You often need to pull out a specific portion of text — the first name from a full name, the area code from a phone number, the year from a date.

• LEFT: returns a given number of characters from the start
• RIGHT: returns a given number of characters from the end
• MID or SUBSTRING: returns characters starting from a specified position for a specified length

3. Finding and Replacing

These functions let you search inside text and optionally replace what you find.

• FIND or INSTR: locates the position of one string inside another
• REPLACE: substitutes all occurrences of a substring with another string
• TRIM: removes extra spaces from the beginning and end of a string

4. Joining and Splitting

• CONCAT or the ampersand (&): joins two or more strings end to end
• SPLIT (in some systems): breaks a string into parts based on a delimiter (like a comma or space)

5. Measuring Length

• LEN or LENGTH: returns the number of characters in a string

Why They Matter

In any real-world data task — whether you are cleaning a customer list, generating reports, validating user input, or preparing data for analysis — you will work with text. String functions give you the power to:

• Standardise messy data (e.g., "john", "John", "JOHN" all become "John")
• Extract meaningful pieces from longer text (e.g., get the domain from an email) …

Let’s begin with something you already know: a stack of plates in a cafeteria. You can only take the top plate off, and you can only put a new plate on top. You never pull a plate from the middle or the bottom. That everyday action is the core idea behind a stack in computer science — a list where all additions and removals happen at one end, called the top.

Now, in your NCERT textbook for Informatics Practices or Computer Science (Class 11 or 12), when you study List Stack Operations, you are learning how to treat a Python list as if it were that stack of plates. A normal list lets you add or remove items from anywhere. But a stack is a restricted list: you can only work with the most recently added item. This restriction is not a weakness — it is a deliberate design that makes certain tasks simple and fast.

The two fundamental operations are:

• Push – adding an element to the top of the stack.
• Pop – removing the top element from the stack.

There is also a third operation, Peek (or Top), which just looks at the top element without removing it. And you will often check if the stack is empty before trying to pop.

Why does this matter? Because stacks are everywhere in real computing. When you press the Back button in a web browser, it pops the previous page off a stack of visited pages. When you undo an action in a word processor, it pops the last change off a stack of edits. Even the way your computer calls one function from another uses a stack behind the scenes. So learning stack operations is not just about lists — it is about understanding a pattern that appears again and again. …