Type Casting & Truthiness

Type Casting is the process of converting an object from one data type to another. Because Python is Strongly Typed, it will not perform risky conversions automatically (like adding a string "5" to a number 5). You must be explicit about your intent.

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1. Implicit vs. Explicit Conversion

Implicit (Automatic)

Python only performs implicit conversion when it is “safe”—meaning no data will be lost. This usually happens when mixing integers and floats.

x = 10    # int
y = 2.5   # float
z = x + y # 12.5 (Python promotes x to float automatically)

Explicit (Manual)

You use the constructor functions of the class you want to convert to.

• int(x): Converts to integer (truncates floats).
• float(x): Converts to floating point.
• str(x): Converts to string.
• bool(x): Converts to boolean.

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2. Truthy and Falsy Values

This is one of the most important concepts in Python logic. Every object in Python has an inherent boolean value. You don’t need a comparison to use an object in an if statement.

The Falsy List

Only these values evaluate to False:

1. Constants: None and False.
2. Zeroes: 0, 0.0, 0j.
3. Empty Collections: "" (empty string), [] (empty list), {} (empty dict), set().

Everything else is Truthy.

truth_check.py

def check(val):
    if val:
        print(f"{repr(val)} is Truthy")
    else:
        print(f"{repr(val)} is Falsy")

check(0)     # Falsy
check(0.1)   # Truthy
check([])    # Falsy
check(" ")   # Truthy (It contains a space!)

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3. Under the Hood: The __bool__ Method

How does Python know if an object is True or False?

When you call bool(obj) or use an object in an if statement, Python follows this priority:

1. It looks for a method named __bool__() on the object’s class and uses its return value.
2. If __bool__ isn’t defined, it looks for __len__(). If the length is 0, it’s False; otherwise, it’s True.
3. If neither exists, the object is always True.

Professional Tip

When defining your own classes later, you can control their “Truthiness” by implementing the __bool__ method.

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4. Common Casting Scenarios

1. Handling User Input

The input() function always returns a str. To do math, you must cast it.

age = int(input("Enter age: "))

2. Truncation vs. Rounding

Casting a float to an int does not round. it simply chops off the decimal (truncation).

print(int(9.99)) # Output: 9

To round properly, use the built-in round() function instead.

3. String Concatenation

You cannot add an int to a str. You must cast the number to a string first.

score = 100
# print("Score: " + score) # TypeError
print("Score: " + str(score)) # Correct

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5. Summary Table

From	To	Method	Result
float	int	int(3.8)	3 (Truncated)
int	float	float(5)	5.0
str	int	int("10")	10
any	str	str(True)	"True"
list	bool	bool([])	False