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Python Variables and Data Types Explained for Beginners (int, float, str, bool)

P2.3 How to Convert Data Types in Python (Type Casting)

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Why. Data from files and forms often arrives as text. Before you can add or average it, you must convert it to a number.

What. Use the type name as a function to convert.

  • int("42") → 42
  • float("19.99") → 19.99
  • str(42) → "42"
  • bool(0) → False, bool(5) → True

How.

Convert safely

  1. Look at the value and its type.
  2. Pick the target type.
  3. Wrap the value: float(value).
  4. Check the new type with type().

Worked example A — Text to number.

Step 1 — What we do. An online form in Dublin sends the amount "120.50" as text. We convert it before adding a €5 fee.

Step 2 — Type and run this code.

amount_text = "120.50"
amount = float(amount_text)
print(amount + 5)

Step 3 — Output you should see.

125.5

Step 4 — What it means. After float(), maths works. Without it, "120.50" + 5 gives an error.

Worked example B — Number to text for a message.

Step 1 — What we do. We build a message for a patient in Nairobi. Text and numbers cannot be joined with + directly.

Step 2 — Type and run this code.

visits = 3
message = "Total visits: " + str(visits)
print(message)

Step 3 — Output you should see.

Total visits: 3

Step 4 — What it means. str() turns 3 into "3" so it can join with other text. Later you will learn f-strings, which are easier.

Worked example C — An intended error: text that is not a number.

Step 1 — What we do. We try to convert text with a comma.

Step 2 — Type and run this code.

print(int("1,200"))

Step 3 — Output you should see.

ValueError: invalid literal for int() with base 10: '1,200'

Step 4 — What it means. Python cannot read the comma. Remove it first: int("1,200".replace(",", "")) gives 1200. You will see this often with Indian formats like "1,25,000".

Ravindra Bagale's Tip

When numbers come with ₹, $ or commas, clean the text first, then convert. Remove symbols with .replace(), then use float().