Unit I: Introduction to Python
1. Basic Elements of Python
Python is a high-level, interpreted programming language known for its readability and simple syntax. The basic elements include character sets and the use of comments to explain code.
- Comments: Used to add notes within the code. Python uses the # symbol for single-line comments.
2. Python Character Set & Tokens
A token is the smallest individual unit in a python program.
- Keywords: Reserved words that have special meaning to the interpreter (e.g., if, else, while).
- Identifiers: Names given to entities like variables, functions, and classes.
- Literals: Constant values stored in variables (e.g., 10, "Hello").
- Operators: Symbols that perform operations on variables and values.
- Punctuators: Symbols used to organize sentence structures and expressions (e.g., , : [ ] { }).
3. Variables, L-values, and R-values
Variables are reserved memory locations to store values.
- L-value: Expressions that refer to a memory location (e.g., a variable on the left side of an assignment).
- R-value: The data value stored at some address in memory (e.g., the value/expression on the right side of an assignment).
4. Knowledge of Data Types
Python provides several built-in data types to handle different kinds of data:
| Category | Data Types |
|---|---|
| Number | Integer, Floating point, Complex |
| Boolean | True, False |
| Sequence | String, List, Tuple |
| Mapping | Dictionary |
| None | Represents the absence of a value |
5. Mutable vs Immutable Types
Understanding mutability is critical for managing data in Python.
- Mutable Types: Values can be changed after they are created (e.g., Lists, Dictionaries, Sets).
- Immutable Types: Values cannot be changed once created (e.g., Numbers, Strings, Tuples).
6. Operators & Expressions
Operators are symbols used to perform computations.
- Arithmetic: +, -, *, /, %, **, //.
- Relational: ==, !=, >, <, >=, <=.
- Logical: and, or, not.
- Assignment: =, +=, -=, *=, /=.
- Identity: is, is not.
- Membership: in, not in.
Precedence of Operators: Determines the order in which operators are evaluated in an expression (e.g., multiplication before addition).
7. Input/Output & Type Conversion
- Input: The
input()function is used to accept data from the console. - Output: The
print()function displays output to the console. - Implicit Conversion: Python automatically converts one data type to another without user involvement.
- Explicit Conversion (Type Casting): The user manually converts the data type using functions like
int(),float(), orstr().
Exam Tips & Warnings
- Division Tip: In Python 3,
/always returns a float, while//(floor division) returns an integer. - Identifier Rules: Identifiers cannot start with a digit and cannot be a keyword.
- Case Sensitivity: Python is case-sensitive; Variable and variable are different.
Frequently Asked Questions
Q: What is the difference between a list and a tuple?
A list is mutable (can be changed), while a tuple is immutable (cannot be changed).
Q: What is a complex number in Python?
It is a number with a real and imaginary part, represented as a + bj.