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Typecasting (Type Conversion)

Typecasting is strictly changing data from one type to another. Python is strict about mixing text and numbers—it won't let us add them together unless we manually convert them first.

Automatic Conversion (Implicit)​

When we do math with different types, Python automatically "upgrades" the "smaller" type to a "larger" one (e.g., adding an integer to a float results in a float) to make sure no data is lost.

a = 7       # whole number (int)
b = 3.5     # decimal (float)

# Python turns 'a' into a decimal before adding them
c = a + b
print(f"Result: {c} | Type: {type(c).__name__}")
Result: 10.5 | Type: float

Manual Conversion (Explicit)​

Use manual casting functions when we need to force a type change, especially when working with user input or mixed data.

The Main Casting Functions​

  • str(): Turns anything into text.
  • int(): Turns text or decimals into a whole number (removes the decimal part).
  • float(): Turns text or whole numbers into a decimal.
user_input = "15"
base_value = 10

# Anti-pattern: This will crash (can't add string and int)
# total = base_value + user_input

# Pythonic: Manually convert the text to a number first
total = base_value + int(user_input)
print(f"Total: {total}")
Total: 25

Avoiding the ValueError Trap​

Trying to turn text into a number will crash our program if the text isn't a standard number (like trying to turn "hello" into 5). When converting text to a whole number, it must look like a standard integer string.

# This works fine
print(int("42"))

# This crashes because of the decimal point
# print(int("42.5"))

# The safe way: convert to a decimal first, then to a whole number
print(int(float("42.5"))) # Result: 42
42
42