1.5 Python Programming Notes

Q1: What is a variable?

A variable is a named container in the computer memory with a meaningful name which can hold a value or data that can be changed.

Q2: How do you initialize, assign, and reassign variable values in Python?

In Python, variables are assigned value using an assignment operator (=) (e.g., myNo = 13).

Initialization means creating a variable for the first time and giving it an initial value.

Reassignment happens when you change the value of an existing variable. When you reassign a variable, you simply overwrite the new value to the variable (e.g., myNo = 12).

Q3: What are data types in programming?

Data types tell the computer what kind of data it is processing. Computers need to know if data is a word, a whole number, or a decimal number to process it correctly.

Q4: What are the three main data types we use in Python?

Commonly used data types in Python are:

Integer (int): Whole numbers without decimals (e.g., 5, -10, 100).
Real / Float (float): Numbers with decimal points (e.g., 2.5, 3.14, -0.01).
String (str): Text, words, or characters enclosed in quotes (e.g., "Hello", "123", "A").

Q5: Why is it important to use the correct data type?

Because computers perform different operations on different types:

If we add two Integers (5 + 5), the computer does Math: result is 10.
If we add two Strings ("5" + "5"), the computer joins them: result is "55".

Using the wrong type can cause errors or incorrect results.

Q6: How do I change data from one type to another (Casting)?

You can "cast" (convert) data using special functions:

int("5") converts the string "5" into the integer 5.
str(10) converts the integer 10 into the string "10".
float(5) converts the integer 5 into the decimal 5.0.

Q7: What are the rules for naming variables in Python?

Must start with a letter or underscore (_).
Cannot start with a number.
No spaces allowed (use _ instead, like my_score).
Case sensitive (Score and score are different variables).

Q8: How do I read data from a user in Python?

We use the input() command to read data from the user in Python.

Syntax:  variable_name = input("Prompt for user: ")
Example: name = input("Enter your name: ")

Note: input() always reads data as a String by default.

Q9: How do I store user input as a Number (Integer)?

Since input() collects Strings, you must cast it if you want to do math.

Syntax: age = int(input("Enter your age: "))

Q10: How do I output data to the screen?

Use the print() command to output data to the screen.

Syntax: print("Hello", name) or print(variable_name)

Q11: What are Arithmetic Operations?

These are symbols used to perform math:

+ (Addition)
- (Subtraction)
* (Multiplication)
/ (Division)
% (Modular)

Q12: What is BIDMAS and how is it implemented in Python?

BIDMAS is a rule that tells you the correct order to solve math problems in Python: Brackets, Indices, Division, Multiplication, Addition, and Subtraction.

B — Brackets ( ) are solved first.
I — Indices (powers or exponents) like 2**3 are solved second.
D & M — Division / and Multiplication * come next, working from left to right.
A & S — Addition + and Subtraction - are done last, also from left to right.

Example 1: Without brackets

result_1 = 2 + 3 * 4  # Python does 3 * 4 first (12), then adds 2
print(result_1)       # Output: 14

Example 2: With brackets

result_2 = (2 + 3) * 4  # Brackets force Python to do 2 + 3 first (5)
print(result_2)         # Output: 20

Example 3: With indices (powers)

result_3 = 2 + 3 ** 2   # Python calculates 3 ** 2 first (9), then adds 2
print(result_3)         # Output: 11

Q13: What are Comparison Operations?

These symbols compare two values and return either True or False:

== (Equal to)
!= (Not equal to)
> (Greater than)
< (Less than)
>= (Greater than or equal to)
<= (Less than or equal to)

Q14: How do I write a simple IF-ELSE statement?

This is used when there are two possible paths.

Syntax:
if condition:
    do these steps if the condition is true
else:
    do these steps if the condition is false

Example:

if age >= 18:
    print("You are an adult.")
else:
    print("You are a child.")