Data Types in Python

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Data Types in Python

In Python, data types define the kind of value a variable can hold and the operations that can be performed on it. They act as blueprints, specifying how data is stored and manipulated in your programs.

Video: Variables in Python

1. Numeric Types:

- `int`: Stores whole (non-decimal) numbers, like `10`, `-5`, or `9999`.
- `float`: Represents floating-point numbers with decimals, like `3.14`, `-2.5e2` (scientific notation), or `1.2345678901234567` (limited precision).
- `complex`: Holds complex numbers with a real and imaginary part, like `3+2j` or `1.5-4.7j`.

# Integer (int) to store age
age = 25

# Float (float) to store price with decimals
price = 14.99

# Complex number (complex) - not as common in everyday use
complex_num = 3 + 2j  # Imaginary unit represented by j

2. String Type:

- `str`: Represents textual data enclosed in single or double quotes, such as `"Hello, world!"`, `'This is a string'`, or multi-line strings using triple quotes (''' or """).

# String (str) to store a name
name = "Alice"

# String with a sentence
greeting = "Hello, how are you?"

# Multi-line string using triple quotes
message = """This is a message
that spans multiple lines."""

3. Boolean Type:

- `bool`: Represents logical values: `True` or `False`. Used for conditional statements and boolean expressions.

Example #1: Exploring Boolean Values and Type Checking with isinstance() and bool() functions

# Boolean (bool) for a true/false condition
is_raining = True

# Using booleans in an if statement
if is_raining:
    print("Bring an umbrella!")

Why Use Data Types?

video: 3 Reasons Why Are Data Types So Important in Python

Data types are essential in Python for several reasons:

Memory Management: Different data types use memory in different ways. Knowing the type helps Python allocate the right amount of memory. For example, an integer requires less space than a string or a list.
- video: How to Get the Size of an Object in Bytes | Python Tutorial for Beginners
Type Safety: Data types help prevent errors by ensuring operations are compatible with the data being used. You can’t add a string to an integer, for instance.
Readability: Using appropriate data types makes code easier to understand. It’s clear what kind of data a variable holds and how it can be used.
Performance: Python can optimize certain operations based on the data type. For example, mathematical calculations on integers are faster than on floats.

Understanding Dynamic Variables in Python with Examples

video: Is Python a Dynamic Language?

Python is a dynamically typed language. This means that the Python interpreter does type checking only as code runs, and the type of a variable is allowed to change over its lifetime.[1]
In Python, variables are dynamic, meaning they can change types during the execution of a program. This flexibility allows you to assign a value of any type to a variable and later reassign it to a value of a different type without any issues. This dynamic nature of variables is due to Python being a dynamically typed language.

Example #: Dynamic Variables in Python

# Initial assignment of an integer value
x = 10
print(x)  # Output: 10
print(type(x))  # Output: <class 'int'>

# Reassigning a string value to the same variable
x = "Hello, World!"
print(x)  # Output: Hello, World!
print(type(x))  # Output: <class 'str'>

# Reassigning a list to the same variable
x = [1, 2, 3]
print(x)  # Output: [1, 2, 3]
print(type(x))  # Output: <class 'list'>

# Reassigning a float value to the same variable
x = 3.14
print(x)  # Output: 3.14
print(type(x))  # Output: <class 'float'>

In this example:

x is initially assigned an integer value of 10.
x is then reassigned a string value "Hello, World!".
x is later reassigned a list [1, 2, 3].
Finally, x is reassigned a float value 3.14.

Each time, the type of x changes dynamically to match the type of the value assigned to it. This flexibility is one of the powerful features of Python, allowing for more concise and adaptable code.

None

In Python, None is a special constant that represents the absence of a value or a null value. It is an object of its own datatype, called NoneType.

Examples:

Assigning None to Variables:
```
a = None
```

Checking for None:

if a is None:
    print("a is None")
else:
    print("a is not None")

Type Hints

In Python, type hints allow you to specify the expected data types of variables, function parameters, and return values. They make the code more readable and help developers understand what kind of values are expected.

Here’s how you can use type hints in Python:

1. Type Hinting for Variables

You can add type hints to variables by using a colon : after the variable name, followed by the type:

Example: Type Hinting for Variables

age: int = 25
name: str = "Alice"
height: float = 5.7
is_student: bool = True

2. Type Hinting in Functions

For functions, type hints are added after the parameter names and before the return type with ->.

Example: Type Hinting in Functions

def greet(name: str) -> str:
    return f"Hello, {name}!"

# Usage
print(greet("Alice"))  # Output: Hello, Alice!

This code specifies that the name parameter should be a str, and the function should return a str.

3. Type Hints for Collections

For more complex types like lists, dictionaries, sets, and tuples.

Lists

To specify that a list contains elements of a certain type, use list.

# A list of integers
numbers: list[int] = [1, 2, 3, 4, 5]

# A list of strings
names: list[str] = ["Alice", "Bob", "Charlie"]

Dictionaries

For dictionaries, you can specify the types of both keys and values using dict.

Example:

# A dictionary with string keys and integer values
age_map: dict[str, int] = {"Alice": 30, "Bob": 25, "Charlie": 35}

Sets

To specify the type of elements in a set, use Set.

Example:

# A set of strings
unique_names: set[str] = {"Alice", "Bob", "Charlie"}

Functions with Collection Type Hints

You can also use type hints in function definitions to specify the types of parameters and return values.

Example:

# Function that processes a list of integers and returns a dictionary
def process_data(numbers: list[int]) -> dict[str, int]:
    result = {
        'sum': sum(numbers),
        'count': len(numbers)
    }
    return result

data = [1, 2, 3, 4, 5]
processed_data = process_data(data)
print(processed_data)  # Output: {'sum': 15, 'count': 5}

Using type hints doesn’t enforce types at runtime but can improve code readability and help detect type-related issues with tools like mypy.

Key Terms

Fix the error

Incorrect Input Conversion [Python Quiz #64]

age = input("Enter your age: ")  
result = age * 2

True/False (Mark T for True and F for False)

In Python, the type of a variable is determined at runtime.

Answer Key (True/False):

True

Multiple Choice (Select the best answer)

What is the output of the following code? [Python Quiz #22]

age = 25
print("I am " + str(age) + " years old.")

A) I am 25 years old.
B) I am “25” years old.
C) Syntax error
D) I am years old. (with quotes)

Watch this video for the answer:https://youtube.com/shorts/DBC5-ZYoGXI?si=PXk-CPGymx2Q6X2p

age = 25
message = "You are " + str(age) + " years old."
message += " Welcome!"
print(message)

Which function would you use to determine the type of a variable in Python?
- A) id()
- B) type()
- C) str()
- D) isinstance()
Which of the following is not a scalar data type in Python?
- A) bool
- B) int
- C) float
- D) list
Which data type is used to represent decimal numbers in Python?
- A) int
- B) float
- C) complex
- D) str
Which of the following is an example of a boolean value in Python?
- a. “True”
- b. 1
- c. 3.14
- d. False
Which scalar data type is used to represent textual data in Python?
- a. str
- b. char
- c. text
- d. string
What is the default type of a numerical literal without a decimal point in Python?
- a. int
- b. float
- c. complex
- d. bool
What is the result of the expression type(“Hello, World!”) in Python?
- A) <class ‘str’>
- B) <class ‘bool’>
- C) <class ‘int’>
- D) <class ‘float’>
What is the output of type(42)?
- A) <class ‘str’>
- B) <class ‘bool’>
- C) <class ‘int’>
- D) <class ‘float’>
What is the result of 3 + 4.5?
- a. 7
- b. 7.5
- c. Error
- d. None of the above
How do you create a string in Python?
- A) Using single quotes (‘)
- B) Using double quotes (“)
- C) Both a and b
- D) None of the above
Which of the following is a valid boolean value in Python?
- a. True
- b. False
- c. 0
- d. All of the above
What is the output of str(3.14)?
- a. 3.14
- b. ‘3.14’
- c. Error
- d. None of the above
What is the result of the following expression? [Python Quiz #79]

type(3 + 4.0)

- A) <class 'str'>
- B) <class 'bool'>
- C) <class 'int'>
- D) <class 'float'>

Which of the following is a correct way to declare a complex number in Python?
- A) a = 3 + 4j
- B) a = 3.4j
- C) a = 3 + 4i
- D) a = 3 + 4
Which function can be used to convert a float to an integer in Python?
- A) float()
- B) int()
- C) str()
- D) bool()
Which of the following statements is true regarding dynamic typing in Python?
- A) Variables can only be assigned values of the same type.
- B) The data type of a variable is determined at runtime based on the value it holds.
- C) Variables must be declared with a specific type.
- D) Once a variable is assigned a type, it cannot be changed.
In Python, what happens if you assign a new value of a different type to a variable?
- A) Python will raise a type error.
- B) Python will change the variable’s type to match the new value.
- C) Python will ignore the new value.
- D) Python will convert the value to the original type.
What is the output of the following code? [Python Quiz #80]

x = 10
x = "Hello"
print(type(x))

- A) <class 'int'>
- B) <class 'str'>
- C) <class 'bool'>
- D) <class 'float'>

What is the result of the following code?

x = 5
x = 5.0
x = True
x = "Python"
print(x)

- A) 5
- B) 5.0
- C) True
- D) Python

What is the main advantage of dynamic typing in Python?
- A) Faster execution time.
- B) More flexibility in code.
- C) Improved error detection at compile-time.
- D) Reduced memory usage.
Which of the following best describes a dynamically typed language?
- A) Type checking is performed during code compilation.
- B) Type checking is deferred until program execution.
- C) Type checking is not performed at all.
- D) Types are always explicitly declared by the programmer.
In Python, which of the following is true about variable assignment?
- A) The type of the variable is determined when the variable is first assigned a value.
- B) The type of the variable is determined at compile-time.
- C) Variables must be explicitly typed before assignment.
- D) Variables cannot change type once assigned.
What is the output of the following code? [Python Quiz #81]

x = "10"
x = int(x) + 2
print(x)

- A) "102"
- B) 102
- C) 12
- D) "12"

Fill in the Blanks

Answer Key (Fill in the Blanks):

Exercises

Exercise 1: Variable Assignment and Basic Operations

Assign the value 5 to a variable named x.
Assign the value 10 to a variable named y.
Assign the sum of x and y to a variable named sum_xy.
Print the value of sum_xy.

Solution:

x = 5
y = 10
sum_xy = x + y
print("Sum of x and y:", sum_xy)

Exercise 2: Working with Different Data Types

Assign a floating-point number to a variable named pi.
Assign a string to a variable named greeting.
Assign a boolean value to a variable named is_active.
Print the types and values of pi, greeting, and is_active.

Solution:

pi = 3.14
greeting = "Hello, World!"
is_active = True

print("Type of pi:", type(pi), "Value:", pi)
print("Type of greeting:", type(greeting), "Value:", greeting)
print("Type of is_active:", type(is_active), "Value:", is_active)

Exercise 3: String Concatenation

Assign your first name to a variable named first_name.
Assign your last name to a variable named last_name.
Concatenate first_name and last_name with a space in between and assign the result to a variable named full_name.
Print the value of full_name.

Solution:

first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print("Full name:", full_name)

Exercise 4: Boolean Operations

Assign the value True to a variable named is_sunny.
Assign the value False to a variable named is_raining.
Create a new variable named can_go_outside that is True if is_sunny is True and is_raining is False.
Print the value of can_go_outside.

Solution:

is_sunny = True
is_raining = False
can_go_outside = is_sunny and not is_raining
print("Can go outside:", can_go_outside)

Exercise 5: Type Conversion

Assign the string "123" to a variable named num_str.
Convert num_str to an integer and assign it to a variable named num_int.
Print the type and value of num_int.

Solution:

num_str = "123"
num_int = int(num_str)
print("Type of num_int:", type(num_int), "Value:", num_int)

Review Questions

Basic Data Types

What are the basic data types in Python?
- Answer: Python’s basic data types include:
  1. Numbers: Integers (int), floating-point numbers (float), and complex numbers (complex).
  2. Text: Strings (str) to represent sequences of characters.
  3. Logical Values: Booleans (bool) for True or False.
How do you create a string in Python? Give an example.
What is the difference between an integer and a float in Python?
How do you convert a string to an integer in Python?
How can you convert a string to an integer and an integer to a string in Python? Provide examples.
What function would you use to find the type of a variable in Python?
What is the purpose of the type() function in Python?

Boolean and None

What are the Boolean values in Python?
What does the None type represent in Python?
- Answer: In Python, the None type represents the absence of a value or a null value. It is a built-in constant that is used to denote a lack of value or a null reference.
- Characteristics of None
  1. Singleton: None is a singleton in Python, meaning there is only one instance of None in a Python runtime. All occurrences of None point to the same object.
    a = None b = None print(a is b) # Output: True
  2. Type: The type of None is NoneType.
    print(type(None)) # Output: <class 'NoneType'>
  3. Boolean Context: None is treated as False in a boolean context.
    if not None: print("None is considered False") # Output: None is considered False
- Checking for None
- To check if a variable is None, use the is operator, as it checks for identity.
```
  variable = None
  if variable is None:
      print("Variable is None")  # Output: Variable is None
```
How do you check if a variable is None?
- Answer: To check if a variable is None in Python, you should use the is operator. The is operator checks for identity, meaning it checks whether two references point to the same object. Since None is a singleton in Python (there is only one instance of None in a Python runtime), using is is the correct and most efficient way to check for None.

variable = None

if variable is None:
    print("Variable is None")

Type Casting

How do you convert an integer to a string in Python?
What is the result of int(‘123.45’)?
What does the str() function do?
How do you safely convert a string to a float, considering the possibility of invalid input?

References and Bibliography

[1]R. Python, “Dynamic vs Static – Real Python,” realpython.com. https://realpython.com/lessons/dynamic-vs-static/ [2]Python Software Foundation, “Built-in Types — Python 3.12.1 documentation,” Python.org, 2019. https://docs.python.org/3/library/stdtypes.html [3]“PEP 526 – Syntax for Variable Annotations | peps.python.org,” peps.python.org. https://peps.python.org/pep-0526/ ‌ ‌ ‌

Learn with Yasir

Data Types in Python

1. Numeric Types:

2. String Type:

3. Boolean Type:

Why Use Data Types?

Understanding Dynamic Variables in Python with Examples

None

Type Hints

1. Type Hinting for Variables

Example: Type Hinting for Variables

2. Type Hinting in Functions

Example: Type Hinting in Functions

3. Type Hints for Collections

Lists

Dictionaries

Example:

Sets

Example:

Functions with Collection Type Hints

Example:

Key Terms

Fix the error

True/False (Mark T for True and F for False)

Multiple Choice (Select the best answer)

Fill in the Blanks

Exercises

Exercise 1: Variable Assignment and Basic Operations

Exercise 2: Working with Different Data Types

Exercise 3: String Concatenation

Exercise 4: Boolean Operations

Exercise 5: Type Conversion

Review Questions

Characteristics of `None`

Checking for `None`

References and Bibliography

Data Types in Python

1. Numeric Types:

2. String Type:

3. Boolean Type:

Why Use Data Types?

Understanding Dynamic Variables in Python with Examples

None

Type Hints

1. Type Hinting for Variables

Example: Type Hinting for Variables

2. Type Hinting in Functions

Example: Type Hinting in Functions

3. Type Hints for Collections

Lists

Dictionaries

Example:

Sets

Example:

Functions with Collection Type Hints

Example:

Key Terms

Fix the error

True/False (Mark T for True and F for False)

Multiple Choice (Select the best answer)

Fill in the Blanks

Exercises

Exercise 1: Variable Assignment and Basic Operations

Exercise 2: Working with Different Data Types

Exercise 3: String Concatenation

Exercise 4: Boolean Operations

Exercise 5: Type Conversion

Review Questions

Characteristics of None

Checking for None

References and Bibliography

Characteristics of `None`

Checking for `None`