Type casting in Python

Type casting, also known as type conversion, is converting a variable from one data type to another. Here are some simple to interesting examples of type casting in Python:


Type casting, also known as type conversion, is the process of converting a variable from one data type to another.

Here are some simple to interesting examples of type casting in Python:

Integer to Float:

x = 5 
y = float(x)

Float to Integer:

z = 10.75
w = int(z)

Integer to String:

age = 25 
age_str = str(age)

String to Integer:

num_str = "42" 
num = int(num_str)

Float to String:

height = 5.9 
height_str = str(height)

String to Float:

weight_str = "68.5" 
weight = float(weight_str)

List to Tuple:

numbers_list = [1, 2, 3, 4, 5] 
numbers_tuple = tuple(numbers_list)

Tuple to List:

coordinates_tuple = (3, 4) 
coordinates_list = list(coordinates_tuple)

String to List of Characters:

word = "hello" 
char_list = list(word)

List of Strings to String:

words_list = ["Hello", "World"] 
sentence = ' '.join(words_list)

Integer to Boolean:

<code>num = 0 is_valid = bool(num)</code>

Boolean to Integer:

is_valid = True 
num = int(is_valid)

String to Boolean:

flag_str = "True" 
flag = bool(flag_str)

Boolean to String:

is_valid = False 
flag_str = str(is_valid)

Floating-Point to Complex:

real_part = 3.0 
imaginary_part = 4.0 
complex_number = complex(real_part, imaginary_part)

String to Date:

from datetime import datetime 
date_str = "2022-01-08" 
date_object = datetime.strptime(date_str, "%Y-%m-%d").date()

Some Interesting Examples:

Using type casting to check user input:

age_str = input("Enter your age: ") 
try: 
  age_int = int(age_str) 
  # Proceed with age-related calculations 
except ValueError: 
  print("Invalid age entered. Please enter a number.")

Converting lists of strings to numbers for calculations:

numbers_str = ["1", "2", "3", "4"] 
numbers_int = [int(num) for num in numbers_str] # List comprehension for conversion 
    total = sum(numbers_int) # Calculate the sum of the numbers

Creating custom objects with string representation:

class Person: 
  def __init__(self, name, age): 
    self.name = name 
    self.age = age 
  def __str__(self): 
    return f"Name: {self.name}, Age: {self.age}" 

person = Person("Alice", 30) 
person_str = str(person) # person_str will now be "Name: Alice, Age: 30"

Handling User Input Flexibly:

age_str = input("Enter your age: ")
# Handle potential string input 
# and convert to integer

age = int(age_str)  
print("You are", age, "years old.")

Converting ASCII Characters to Codes and Vice Versa:

char = "A"
code = ord(char)  # Convert character to its ASCII code
print(code)  # Output: 65

code = 97
char = chr(code)  # Convert ASCII code to its corresponding character
print(char)  # Output: 'a'

These examples demonstrate various type casting operations in Python. Understanding how to convert between different data types is essential for working with diverse data in Python programs.

Some common mistakes developers make while using type casting in Python:

Assuming Success Without Verification:

  • Mistake: Assuming that a cast will always succeed, leading to unexpected errors if the conversion fails.
  • Example: int("hello") will raise a ValueError because “hello” cannot be converted to an integer.
  • Best Practice: Use try...except blocks to handle potential casting errors.

Confusing int() and float():

  • Mistake: Using int() to convert a string that contains a decimal point, resulting in truncation of the decimal part.
  • Example: int("3.14") will produce 3, not 3.14.
  • Best Practice: Use float() for strings containing decimal values.

Overlooking Data Loss:

  • Mistake: Casting a wider data type (e.g., float) to a narrower one (e.g., int) without considering the potential loss of precision.
  • Example: int(3.99) will result in 3, losing the decimal part.
  • Best Practice: Be mindful of data loss and consider rounding or other techniques if precision is crucial.

Incorrect String Formatting:

  • Mistake: Using string formatting with incorrect types, leading to type errors or unexpected results.
  • Example: "The value is %d" % "hello" will fail because “hello” is a string, not an integer.
  • Best Practice: Ensure data types align with placeholders in string formatting expressions.

Implicit Conversion Pitfalls:

  • Mistake: Relying too heavily on Python’s implicit type conversions, potentially masking errors or causing unexpected behavior.
  • Example: Comparing a string and a number using == might work due to implicit conversion, but it’s not always reliable.
  • Best Practice: Be explicit about type conversions using built-in functions like int()float()str(), etc.

Missing Type Checks:

  • Mistake: Not verifying data types before performing operations, leading to type errors and crashes.
  • Example: Trying to add a string and a number will result in a TypeError.
  • Best Practice: Use isinstance() or type() to check data types before operations.

Infinite Recursion with Custom Classes:

  • Mistake: Implementing the __str__ method in a custom class that calls str() on itself, causing infinite recursion.
  • Best Practice: Avoid calling str() on the object itself within __str__.

Overlooking Inheritance Issues:

  • Mistake: Assuming that type casting works the same way with inherited classes, leading to errors when assumptions don’t hold.
  • Example: Casting a subclass instance to its parent class might fail if the subclass overrides certain methods.
  • Best Practice: Be aware of inheritance hierarchies and potential casting issues.

By understanding these common mistakes and following best practices, you can write more robust and reliable Python code that utilizes type casting effectively.

Type Casting Quiz

What is the output of int(3.14)?

  • A. 3.14
  • B. 3
  • C. Error

The answer is B. 3

What is the output of float(’10’)?

  • A. 10
  • B. 10.0
  • C. Error

The answer is B. 10.0

What is the output of str(True)?

  • A. True
  • B. ‘True’
  • C. Error

The answer is B. ‘True’

What is the output of bool(“hello”)?

  • A. True
  • B. False
  • C. Error

The answer is A. True

What is the output of bool(0)?

  • A. True
  • B. False
  • C. Error

The answer is B. False

What is the output of bool(“0”)?

  • A. True
  • B. False
  • C. Error

The answer is A. True