Oct 04, 2023 8 mins

Python Variables and Data Types

Python Variables and Data Types Python Variables and Data Types

Python is widely used programming language across various fields from web development to data science. One of the fundamental aspects of leaning Python is understanding its variables and data types. This lession will guide you through the basics of Python variables, different data types available, and practical examples to help you to start with Python programming.

What are Variables in Python?

Variables are essential in Python as they store data values that your programs can manipulate. Unlike some other programming languages, Python does not require explicit declaration of variable to reserve memory space. The declaration happens automatically when you assign a value to a variable. For example, if you set x = 10, Python understands that x is an integer type without needing an explicit declaration.

Declaring and Using Variables in Python

When you start writing Python code, the way you name and handle variables can significantly affect the readability and functionality of your code. Python uses dynamic typing, which means you can reassign variables to different data types of variable. This feature is useful but can lead to type-related errors if not managed carefully. Consider the following code snippet for example.

x = 10         # Here x is an integer
x = "ten"      # Now x is a string of text

The code starts with x = 10, which means x is an integer at first. Then x = “ten” is used, whom changes x to a string. This flexibility is powerful, but it requires that you, who write the code, keep track of how variables are used to prevent type-related errors.

Python Naming Conventions

Using good naming conventions is essential for writing clear and maintainable code. Here are the major rules for Python Naming Conventions

  • Use Clear and Descriptive Names: Choose names that describe the purpose of the variable. Ex: total_price, email_address, first_name.
  • Avoid Single Character Names: Except for counters or temporary variables, avoid single letters which can be ambiguous.
  • Use Snake Case: Python convention prefers snake_case where words are lowercase with underscores between them. Ex: customer_address.

Variables Naming in Python

Variables should be named in a way that describes their purpose using lowercase letters with words separated by underscores. (This style is often referred to as snake_case).

# Good variable names
account_balance = 1000
email_address = ""
temperature_celsius = 22.5

# Poor variable names
a = 1000  # What does 'a' stand for?
emAdd = ""  # Mixed case and abbreviations make it unclear
t = 22.5  # Unclear what 't' represents

Functions Naming in Python

Functions should also use snake_case and typically start with a verb to indicate the action they perform. The name should clearly reflect what the function does.

# Good function names
def calculate_total_price(quantity, price):
    return quantity * price

def send_email(recipient, message):
    # Code to send an email

# Poor function names
def price(x, y):  # What does this function calculate?
    return x * y

def mail(a, b):  # What does 'mail' do exactly?

Classes Naming in Python

Class names in Python should follow the CapWords convention where each word starts with a capital letter and no underscores are used. This is often referred to as CamelCase.

# Good class names
class ShoppingCart:

class EmailSender:

# Poor class names
class shoppingcart:  # Should be CamelCase

class email:  # Does not clearly describe what the class represents


Constants are typically defined at the top level of a module and should be written in all uppercase letters with underscores separating words.

# Good constant names

# Poor constant names
max = 100  # Not clear it's a constant, name should be all uppercase
TIMEOUT = 5  # Good, but could be more descriptive

These conventions ensure that your code is easier to read and understand which is particularly important when working in teams or when others need to read your code in the future.

Python Data Types Explained

Python variables can hold different types of data. Understanding these types is essential for efficient programming. Python’s standard mutable and immutable data types include integers, floats, strings, lists, dictionaries, set, bytearray, tuple, Frozenset and bytes.

Also, these data types can be classified as either immutable or mutable based on whether their values can be changed after they are created.

Python Immutable Data Types

Immutable data types are types of data that cannot be changed after they are created. An integer, which is a whole number, is immutable because it stays the same once set. A float, that is a number with a decimal point, also cannot change. Strings, which are sequences of characters, are immutable too. Tuples, that are ordered collections of elements, cannot be changed after creation. Frozensets, which are immutable sets, stay the same once made. Bytes, whom are sequences of bytes, do not change either. These types are fixed and do not allow changes to their values.

Integers: Perfect for counting or iterations.

x = 10
# x = x + 1 creates a new integer, x itself is not changed

Floats: Used for precision in calculations.

y = 10.5
# y = y + 0.5 creates a new float, y itself is not changed

Strings: Essential for text manipulation.

s = "hello"
# s = s + " world" creates a new string, s itself is not changed

Tuple: An ordered collection of elements that cannot be changed.

my_tuple = (1, 2, 3)
# my_tuple[0] = 10 would raise an error

Frozenset: An immutable version of a set.

my_frozenset = frozenset([1, 2, 3])
# my_frozenset.add(4) would raise an error

Bytes: An immutable sequence of bytes.

my_bytes = bytes([1, 2, 3])
# my_bytes[0] = 10 would raise an error

Python mutable Data Types

Mutable data types are types whose values can change after they are created. Lists, which are ordered and can be changed, are an example. Dictionaries, that are collections of key-value pairs, also belong to this category. Sets, whom contain unique elements, can be changed as well. Bytearrays, which are sequences of bytes, are another mutable data type. These types allow modifications, which means you can add, remove, or change elements after they are made.

lists: Ideal for storing collections of items.

my_list = [1, 2, 3]
my_list[0] = 10  # The first element is now 10

dictionaries: Key-value pairs that store data more complexly

my_dict = {'a': 1, 'b': 2}
my_dict['a'] = 10  # The value for key 'a' is now 10

Set: A collection of unique elements that is unordered and changeable.

my_set = {1, 2, 3}
my_set.add(4)  # The set now contains 1, 2, 3, 4

Bytearray: A mutable sequence of bytes.

my_bytearray = bytearray([1, 2, 3])
my_bytearray[0] = 10  # The first byte is now 10

Python Type Casting

Python type casting is a way to change one data type into another. This is useful when you need a value in a different form. For example, you might have a number stored as a string which you need to use in a math operation. You can change that string into an integer with int(). Type casting includes functions like int(), float(), and str(), which change values into integers, floats, or strings. It is a tool that helps when working with different types of data, whom you need in a certain form for your code to work correctly.

These examples cover common scenarios where type casting is applied across various data types in Python.

Integer to Float

Converting an integer to a float can be useful when you need floating-point precision for calculations.

integer_value = 42
float_value = float(integer_value)
print(float_value)  # Output: 42.0

The code takes an integer value which is 42, and converts it into a float. It does this by using the float function that changes the type of integer_value to a float. This means the integer 42 that was first used has become 42.0 as a float.

Float to Integer

When converting a float to an integer, Python truncates the decimal part.

float_value = 3.99
integer_value = int(float_value)
print(integer_value)  # Output: 3

The float value which is a number with a decimal point is changed into an integer. The integer is made by cutting off the decimal part. The int function, which converts the float keeps only the part before the decimal point.

String to Integer

Converting a string to an integer is common when parsing numbers from textual sources.

string_value = "123"
integer_value = int(string_value)
print(integer_value)  # Output: 123

The code starts with a string which is “123”. This string is then converted into an integer by a function called int, which takes the string as input and changes it to an integer.

String to Float

This conversion is often used when you need to parse strings containing floating-point numbers.

string_value = "123.45"
float_value = float(string_value)
print(float_value)  # Output: 123.45

The string named string_value holds the text “123.45”. This string is then turned into a float by the float() function, which takes the string and converts it to a floating-point number.

Integer to String

Converting numbers to strings is useful when you need to concatenate numerical values with other strings.

integer_value = 500
string_value = str(integer_value)
print(string_value)  # Output: "500"

The code starts with the integer 500 which is stored in the variable named integer_value. This variable is then converted into a string. The function str() is applied to integer_value, which changes the integer into a string.

Float to String

Similar to integers, converting floats to strings is helpful for textual representations.

float_value = 123.45
string_value = str(float_value)
print(string_value)  # Output: "123.45"

The code sets a float value of 123.45. Then, it converts this float value to a string using the function “str”.

List to Tuple

Converting lists to tuples can be necessary when you need an immutable version of a list.

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

The list_value turns this into a tuple named “tuple_value” using the ‘tuple()’ function which transforms lists into tuples.

Tuple to List

Converting tuples to lists is useful when you need a mutable version of a tuple.

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

The line list_value = list(tuple_value) is what turns the tuple into a list. The list() function takes the tuple as an ardument and returns converted list.

String to List

Transforming a string to a list can help when you need to perform operations on each character.

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

The code takes a string, “hello”, and converts it into a list. It does this by using a function called “list” on the string. This function separates each letter in the string into its own item in a list.

List to String

Joining a list of characters into a single string is often needed in data manipulation.

list_value = ['h', 'e', 'l', 'l', 'o']
string_value = ''.join(list_value)
print(string_value)  # Output: "hello"

The code takes a list of letters, like [‘h’, ‘e’, ‘l’, ‘l’, ‘o’], and turns it into a single string. It uses a function called “join” which joins the letters together.

Troubleshooting Common Errors

Understanding common errors can help you debug your code faster. One frequent error is type mismatch, where an operation is applied to an inappropriate type. For instance, adding a number to a string will raise a TypeError. Always check the type of your variables when errors occur.


Getting to grips with variables and data types is a significant first step in becoming proficient in Python. Start by experimenting with different data types and variables, and use the examples in this article to guide your practice.


Q: What is dynamic typing in Python?
A: Dynamic typing means that Python understands the type of a variable at runtime based on the data assigned to it, unlike static typing, where the type is explicitly declared.

Q: Can Python variables change type?
A: Yes, Python variables can be reassigned to different data types, which is a feature of dynamic typing.

Q: What is a type error and how can I avoid it?
A: A type error occurs when an operation is applied to a variable of an inappropriate type, such as adding a string and a number. To avoid type errors, ensure your variables are of the correct type before performing operations on them.


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