Explicit Type Casting

Overview

Python is strongly typed so implicit conversions are rare. Explicit type casting with int(), float(), str(), list(), bool() etc. is required whenever you need to convert between types — common in data processing and API handling.

Syntax

python

# Type conversion functions
int("42")          # 42
int(3.9)           # 3 (truncates, not rounds!)
float("3.14")      # 3.14
str(100)           # "100"
bool(0)            # False
list("abc")        # ['a', 'b', 'c']
tuple([1, 2, 3])   # (1, 2, 3)
set([1, 1, 2, 3])  # {1, 2, 3}

Common Pitfalls

int('3.14') raises ValueError — you must first convert to float: int(float('3.14')).
int(3.9) truncates toward zero, not rounds — use round() for rounding behavior.
Interview tip: Type casting does NOT change the original object — Python creates a new object of the target type.

Real-World Example

Parse and validate incoming JSON API data with proper type casting

example

python

def parse_user_data(raw: dict) -> dict:
    return {
        "id": int(raw.get("id", 0)),
        "name": str(raw.get("name", "")).strip(),
        "age": int(raw.get("age", 0)),
        "active": bool(raw.get("active", False)),
        "scores": list(raw.get("scores", [])),
    }

data = {"id": "42", "name": "  Alice  ", "age": "30", "active": 1}
print(parse_user_data(data))

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