Python Casting

Learn how to convert between different data types in Python using casting.

Specify a Variable Type

There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses classes to define data types, including its primitive types.

Casting in Python is therefore done using constructor functions:

int() - constructs an integer number from an integer literal, a float literal (by removing all decimals), or a string literal (providing the string represents a whole number)
float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)
str() - constructs a string from a wide variety of data types, including strings, integer literals and float literals

Integers

Example

x = int(1)   # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

Floats

Example

x = float(1)     # x will be 1.0
y = float(2.8)   # y will be 2.8
z = float("3")   # z will be 3.0
w = float("4.2") # w will be 4.2

Strings

Example

x = str("s1") # x will be 's1'
y = str(2)    # y will be '2'
z = str(3.0)  # z will be '3.0'

Type Conversion Examples

Converting to Integer

# From float to int
num_float = 9.8
num_int = int(num_float)
print(num_int)  # Output: 9

# From string to int
str_num = "123"
num_int = int(str_num)
print(num_int)  # Output: 123

# From boolean to int
bool_val = True
num_int = int(bool_val)
print(num_int)  # Output: 1

Converting to Float

# From int to float
num_int = 10
num_float = float(num_int)
print(num_float)  # Output: 10.0

# From string to float
str_num = "3.14"
num_float = float(str_num)
print(num_float)  # Output: 3.14

# From boolean to float
bool_val = False
num_float = float(bool_val)
print(num_float)  # Output: 0.0

Converting to String

# From int to string
num_int = 42
str_num = str(num_int)
print(str_num)  # Output: '42'

# From float to string
num_float = 3.14159
str_num = str(num_float)
print(str_num)  # Output: '3.14159'

# From list to string
my_list = [1, 2, 3]
str_list = str(my_list)
print(str_list)  # Output: '[1, 2, 3]'

Common Casting Errors

Be careful when casting, as some conversions may raise errors:

Invalid String to Integer

# This will raise a ValueError
x = int("hello")  # ValueError: invalid literal for int()

Invalid String to Float

# This will raise a ValueError
y = float("abc")  # ValueError: could not convert string to float

Safe Casting with Error Handling

def safe_int_cast(value):
    try:
        return int(value)
    except ValueError:
        print(f"Cannot convert '{value}' to integer")
        return None

# Usage
result = safe_int_cast("123")    # Returns 123
result = safe_int_cast("hello")  # Prints error message, returns None

Advanced Casting

Boolean Casting

# Converting to boolean
print(bool(1))      # True
print(bool(0))      # False
print(bool(""))     # False
print(bool("text")) # True
print(bool([]))     # False
print(bool([1, 2])) # True

List and Tuple Casting

# Converting between list and tuple
my_list = [1, 2, 3, 4]
my_tuple = tuple(my_list)
print(my_tuple)  # (1, 2, 3, 4)

my_tuple = (5, 6, 7, 8)
my_list = list(my_tuple)
print(my_list)   # [5, 6, 7, 8]

# Converting string to list
text = "hello"
char_list = list(text)
print(char_list)  # ['h', 'e', 'l', 'l', 'o']