Python Data Type Conversion

During programming, we often need to convert between different data types. For example, getting numbers from user input (which is always a string), or concatenating numbers into text. Python provides a series of built-in functions to perform these type conversion operations.

This type of type conversion explicitly specified by programmers is called explicit type conversion.

Common Conversion Functions

Converting to Integer: int()

The int() function can create an integer from a float or numeric string.

• Converting from a Float: The decimal part is directly truncated, not rounded.

  x = int(3.14)
  print(x)  # Output: 3
  
  y = int(-5.9)
  print(y) # Output: -5

• Converting from a String: The string must contain only integer numbers.

  age_str = "25"
  age_int = int(age_str)
  print(age_int)  # Output: 25
  
  # int("25.5")  # Raises ValueError because it contains a decimal point
  # int("hello")   # Raises ValueError because it contains non-numeric characters

Converting to Float: float()

The float() function can create a float from an integer or numeric string.

print(float(10))      # Output: 10.0
print(float("123.45")) # Output: 123.45
print(float("-5"))     # Output: -5.0

# float("abc") # Raises ValueError

Converting to String: str()

The str() function can convert almost any object of any other data type to its string representation.

num = 100
pi = 3.14
my_list = [1, 2, 3]

print(str(num))    # Output: '100'
print(str(pi))     # Output: '3.14'
print(str(my_list))# Output: '[1, 2, 3]'

# Common usage: concatenating strings and numbers
message = "My age is " + str(25)
print(message) # Output: My age is 25

Converting to Sequence Types

Converting to List: list()

The list() function can convert an iterable (such as a string, tuple, or set) into a list.

my_str = "hello"
print(list(my_str))  # Output: ['h', 'e', 'l', 'l', 'o']

my_tuple = (1, 2, 3)
print(list(my_tuple)) # Output: [1, 2, 3]

my_set = {1, 2, 3}
print(list(my_set))   # Output: [1, 2, 3] (order may vary)

Converting to Tuple: tuple()

The tuple() function can convert an iterable into a tuple.

my_list = [1, 2, 3]
print(tuple(my_list)) # Output: (1, 2, 3)

Converting to Set: set()

The set() function can convert an iterable into a set. Note that sets will automatically remove duplicate elements.

my_list = [1, 2, 2, 3, 3, 3]
print(set(my_list)) # Output: {1, 2, 3}

Implicit Type Conversion

Besides explicit conversion, Python also automatically performs implicit type conversion in certain situations. This typically happens in operations with different numeric types; Python will "promote" lower-precision types to higher-precision types to avoid data loss.

int_val = 5
float_val = 2.5

result = int_val + float_val  # Python automatically converts int_val to float

print(result)       # Output: 7.5
print(type(result)) # Output: <class 'float'>