🔨 Guided Build #1: Your First Data Dictionary

Let us build a data dictionary together for this simple Python program. Read the code carefully first.

🐍 Simple Greeting Program

name = "Alex"
age = 16
height = 1.75

print("Hello, " + name)
print("Age:", age)
print("Height:", height, "metres")

📋 Step-by-Step: Building the Dictionary

Step 1: Identify every variable

Read through the code and find every variable name. Here we have: name, age, height.

Step 2: Determine the data type of each

Look at the value assigned to each variable:

name = "Alex" → text in quotes → String
age = 16 → whole number, no decimal → Integer
height = 1.75 → number with decimal → Float

Step 3: Work out the format

name: text of varying length → XX..XX
age: a 2-digit number → NN
height: a number like 1.75 → N.NN

❗ IMPORTANT: How to Figure Out Size in Bytes

This is the trickiest part. Here is a simple rule you can follow every time:

Data Type	Size in Bytes Rule	How to Remember
String	1 byte per character (use the max length you allow)	Username up to 15 characters = 15 bytes
Integer (small)	2 bytes	For numbers up to 32,767 (age, level, count)
Integer (large)	4 bytes	For numbers up to ~2 billion (big scores, IDs)
Float	Always 4 bytes	Every float is 4 bytes. Always.
Boolean	1 bit	Just True or False = 1 bit
Date/Time	Always 4 bytes	Stored as 32 bits = 4 bytes

Step 4: Calculate sizes — applying the rules above

name (String): We decide the maximum length is 20 characters. String rule: 1 byte per character → 20 bytes. Display size: 20 characters wide.

age (Integer): Age is a small number (0–99). Small integer rule → 2 bytes. Display size: 2 digits wide.

height (Float): Float rule: always 4 bytes. Display size: 4 characters wide (“1.75”).

Step 5: Write description, example, validation

Think about what each variable is for, give a realistic example, and set sensible rules.

✅ Completed Data Dictionary

Variable	Data Type	Format	Bytes	Display	Description	Example	Validation
name	String	XX..XX	20	20	The person's first name	Alex	1–20 characters, letters only
age	Integer	NN	2	2	The person's age in years	16	Integer between 0 and 99
height	Float	N.NN	4	4	The person's height in metres	1.75	Decimal between 0.50 and 2.50