Type Conversion (Casting)

Converting Between Types

Sometimes you need to change a variable's type. Python makes this easy with conversion functions.

Converting TO String

Use str() to turn anything into text.

age = 28
age_text = str(age)        # "28"

score = 95.5
score_text = str(score)    # "95.5"

result = True
result_text = str(result)  # "True"

Why? When you want to combine numbers with text:

name = "Alice"
age = 28
# This FAILS: print("My name is " + name + age)  ✗
# But this WORKS:
print("My name is " + name + " and I'm " + str(age))  ✓

Converting TO Integer

Use int() to get whole numbers. Decimals are truncated (not rounded)!

score = "95"
score_int = int(score)     # 95

price = 19.99
price_int = int(price)     # 19 (truncated, not rounded!)

bool_value = True
bool_int = int(bool_value) # 1

Converting TO Float

Use float() to get decimal numbers.

age = 28
age_float = float(age)     # 28.0

score = "95.5"
score_float = float(score) # 95.5

Converting TO Boolean

Use bool(). Most values are True, but some are special "falsy" values:

bool(1)        # True
bool(0)        # False  ← special case!
bool("hello")  # True
bool("")       # False  ← empty string is falsy!
bool([])       # False  ← empty list is falsy!

Real-World Example: Calculating Totals

# User input comes as text (strings)
price_str = "19.99"
quantity_str = "3"

# Convert to numbers for math
price = float(price_str)
quantity = int(quantity_str)

# Calculate total
total = price * quantity    # 59.97

# Convert back to string for display
print(f"Total: ${str(total)}")

Insight: This pattern (string → number → string) happens constantly in real programs!