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Types and Conversions

Every value in Python has a type. The type determines what you can do with it.

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See how type conversions change values and what happens when they fail: Open in Python Tutor

Basic types

Type What it holds Examples
str Text (string) "hello", 'world', "123"
int Whole number 42, -3, 0
float Decimal number 3.14, -0.5, 2.0
bool True or False True, False
None Nothing / empty None

Checking a type

print(type("hello"))   # <class 'str'>
print(type(42))        # <class 'int'>
print(type(3.14))      # <class 'float'>
print(type(True))      # <class 'bool'>

Converting between types

Function Converts to Example
str() String str(42) → "42"
int() Integer int("42") → 42
float() Float float("3.14") → 3.14
bool() Boolean bool(0) → False

Why conversion matters

input() always returns a string. If you want to do math with it, you must convert:

age_text = input("Age? ")     # User types 30 → age_text is "30" (string)
age = int(age_text)            # Convert to integer
print(age + 1)                 # 31 (math works now)

Without conversion:

print("30" + 1)  # TypeError: can only concatenate str to str

Truthy and falsy values

Python treats some values as True and others as False in conditions:

Falsy (treated as False):

  • False, 0, 0.0, "" (empty string), [] (empty list), {} (empty dict), None

Truthy (treated as True):

  • Everything else: True, any non-zero number, any non-empty string/list/dict
name = ""
if name:
    print("Has a name")
else:
    print("No name")      # This runs because "" is falsy

Common mistakes

Comparing different types:

"5" == 5     # False! String "5" is not the same as integer 5
int("5") == 5  # True — convert first

Converting non-numeric strings:

int("hello")   # ValueError: invalid literal
int("3.14")    # ValueError: cannot convert float string to int directly
float("3.14")  # 3.14 — use float() for decimal strings

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