Switch Between Types

The problem...

You have a number. But you need text.

You have text. But you need a number.

You have a float. But you need an int.

Types don't always match what you need. And Python won't convert them for you automatically.

The idea!

Python gives you built-in functions to convert values from one type to another.

You decide what type you need. Python does the conversion.

Making it real

You've already seen this — every time you used input().

age = input("Enter your age: ")
print(type(age))   # <class 'str'> — always a string

age = int(age)
print(type(age))   # <class 'int'> — now a number

That's type conversion. One function. One line. Done.

The conversion functions

• int() — converts to integer
• float() — converts to float
• str() — converts to string
• bool() — converts to bool

In practice

# str to int
age = int("25")
print(age)          # 25
print(type(age))    # <class 'int'>

# str to float
height = float("1.75")
print(height)       # 1.75

# int to str
score = str(100)
print(score)        # "100"
print(type(score))  # <class 'str'>

# int to float
price = float(5)
print(price)        # 5.0

# float to int — truncates
result = int(3.9)
print(result)       # 3 — not 4

Going further — bool()

Almost everything converts to True. Very few things convert to False.

print(bool(1))      # True
print(bool(0))      # False
print(bool("Bull")) # True
print(bool(""))     # False — empty string
print(bool(3.14))   # True
print(bool(0.0))    # False

The rule: empty, zero, and nothing convert to False. Everything else is True.

What's really happening

Python doesn't guess. When you mix types, it throws an error.

Type conversion is you telling Python explicitly: "treat this value as this type."

Heads up!

• int("25") works — int("Bull") throws a ValueError
• int(3.9) truncates — use round() if you need rounding
• bool(0) is False — useful to know, you'll see this in Control Flow
• Always convert input() before doing math

The mindset shift

Stop thinking: "Python should figure out the type."

Start thinking: "I know what type I need. I convert explicitly."

What you should understand now

• int(), float(), str(), bool() convert between types
• You can only convert compatible values — int("Bull") fails
• Empty and zero values convert to False — everything else to True
• Always convert input() before doing math