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Python Type Casting

Type casting is like pouring juice from a cup into a bottle: the drink stays the same but the container changes. You turn a value such as the text 5 into the number 5 so you can do math with it.

In this page:

  1. Converting to int
  2. Converting to float
  3. Converting to str
  4. Converting to bool
  5. Converting Between Collections
Syntax
python 
int(value)
float(value)
str(value)
bool(value)

Converting to int

Wrapping a value in int() converts it to a whole number, truncating any decimal part of a float rather than rounding it — int(9.8) gives 9, not 10.

Passing a numeric string like int(42) works fine, but int(abc) raises a ValueError since there's no digit sequence to parse.

Example: Converting to int

python 
print(int(9.8))
print(int("42"))

Converting to float

float() turns an int or a numeric string into a floating-point number, which is useful whenever you need decimal precision for calculations like averages or percentages. float('3.14') and float(3) both work, but float(three) fails the same way int() does on non-numeric text.

Example: Converting to float

python 
print(float("3.14"))
print(float(3))

Converting to str

str() turns any value — a number, a list, a boolean — into its text representation, which is essential whenever you need to concatenate that value into a message with the + operator, since Python won't silently mix strings and numbers.

Printing already converts values for you, but explicit str() is needed for manual string building.

Example: Converting to str

python 
age = 30
message = "Age: " + str(age)  # str() converts the int so it can be concatenated
print(message)

Converting to bool

bool() reduces any value down to True or False using Python's truthiness rules — zero, None, and empty containers become False, and virtually everything else becomes True.

This conversion happens automatically inside an if condition, so understanding it explains why if my_list: works without comparing to an explicit length.

Example: Converting to bool

python 
print(bool(0))  # 0 is falsy
print(bool([]))  # empty list is falsy
print(bool("hello"))  # non-empty string is truthy

Converting Between Collections

list(), tuple(), and set() can convert between collection types and other iterables — set() is particularly handy for removing duplicates from a list, since converting to a set drops repeats and converting back to a list restores an ordinary sequence.

These conversions build a brand new object rather than modifying the original in place.

Example: Converting Between Collections

python 
numbers = [1, 2, 2, 3, 3]
unique = list(set(numbers))  # set() drops duplicates, list() converts back to a list
print(unique)
Related Topics

Python Type Hints · Python Constants · Python Booleans · Python Variables

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Common Mistakes
  1. Expecting int(9.8) to round to 10; it truncates toward zero and gives 9 (use round()).
  2. Calling int("3.5") directly, which raises ValueError; convert with int(float("3.5")).
  3. Assuming bool("False") is False; any non-empty string is truthy, so it is True.
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