Data types and variables in python

Python variables and Python data Types

The rules for naming Variable in python

In Python, there are some rules for naming variables:

1. Variable names must start with a letter or an underscore character (_). They cannot start with a number.

2. Variable names can contain letters, numbers, and underscores.

3. Variable names are case-sensitive, which means that message and Message are different variables.

4. Variable names cannot be a reserved keyword in Python, such as if, else, while, for, etc.

Here are some examples of valid and invalid variable names in Python:

Valid variable names in python:

message
_message
message1
my_message
_my_message

Invalid variable names in python:

1message # Cannot start with a number
my-message # Cannot contain a hyphen
my message # Cannot contain spaces
if # Cannot be a reserved keyword

How to declare Variables in python?

In Python, you do not need to declare variables before using them. You can simply assign a value to a variable, and Python will create the variable for you.

When naming variables in Python, it’s a good practice to use descriptive and meaningful names that reflect the purpose of the variable. This makes your code more readable and understandable for yourself and others who might read your code.

Multi Words Variable Names in python with examples

When naming variables in Python, it’s common to use multi-word names to make the variable name more descriptive and readable. There are two common ways to create multi-word variable names in Python: using underscores or using camel case.

Underscores in Python:

This involves separating the words in the variable name using underscores (_).

For example:

first_name
last_name
age_of_person
my_variable_name

Camel case in Python:

This involves capitalizing the first letter of each word in the variable name except the first word.

For example:

firstName
lastName
ageOfPerson
myVariableName

Both methods are valid in Python, and which one to use is mostly a matter of personal preference. However, the convention in Python is to use underscores to separate words in variable names.

It’s important to note that regardless of the method used, variable names should be descriptive and meaningful to help make the code more readable and understandable.

How to create  Variables in python ?

In Python, variables are used to store data values. Unlike other programming languages, Python does not require you to declare a variable before using it. To create a variable in Python, you simply assign a value to a name using the equals sign (=) operator.

Here are some examples of creating variables in Python:

Code:

# Create a variable called "name" and assign it a string value
name = "Gogo"

# Create a variable called "age" and assign it an integer value
age = 30

# Create a variable called "salary" and assign it a floating-point value
salary = 1000.50

# Create a variable called "is_employee" and assign it a boolean value
is_employee = True

In this code:

1-we create four variables with different data types.

2-The first variable, “name”, is a string variable that stores the value “John”.

3-The second variable, “age”, is an integer variable that stores the value 30.

4-The third variable, “salary”, is a floating-point variable that stores the value 1000.50.

5-The fourth variable, “is_employee”, is a boolean variable that stores the value True.

Once you have created a variable, you can use it in your code by referencing its name.

For example, you can print the value of a variable using the print() function:

print(name)
print(age)
print(salary)
print(is_employee)

Many Values to Multiple Variables in python

• In Python, you can assign multiple values to multiple variables using a technique called “unpacking”.
• This allows you to assign multiple values to multiple variables in a single line of code.

Here’s an example:

# Assigning multiple values to multiple variables
name, age, city = "John", 25, "New York"

# Printing the variables
print(name) # Output: John
print(age) # Output: 25
print(city) # Output: New York

In this example:

1-we define three variables name, age, and city and assign them values “John”, 25, and “New York”, respectively.

2-We use commas to separate the variable names and values, and the order of the variables corresponds to the order of the values.

3-When we print the variables, we can see that each variable contains the correct value.

notes:

It’s important to note that the number of variables on the left side of the assignment operator (=) must match the number of values on the right side.

If there are more variables than values, Python will raise a ValueError exception.

If there are more values than variables, Python will ignore the extra values.

One Value to Multiple Variables in python

• In Python, you can assign the same value to multiple variables in a single line of code.
• This can be useful when you want to create multiple variables that contain the same value.

Here’s an example:

# Assigning the same value to multiple variables
x = y = z = 10

# Printing the variables
print(x) # Output: 10
print(y) # Output: 10
print(z) # Output: 10

In this example:

1-we define three variables x, y, and z and assign them all the value 10 in a single line of code.

2-When we print the variables, we can see that each variable contains the correct value.

Note that :

• When you assign the same value to multiple variables, all the variables reference the same object in memory.
• This means that changing the value of one variable will also change the value of the others.

For example:

# Changing the value of one variable
x = 20

# Printing the variables
print(x) # Output: 20
print(y) # Output: 10
print(z) # Output: 10

In this example:

we change the value of the x variable to 20. When we print the variables, we can see that x contains the new value, but y and z still contain the original value.

The  data types in python:

In Python, there are several data types that can be used to create variables. Here are some examples of creating variables for each of the data types in Python:

Python Integer variables

To create integer variable in python

# Create an integer variable
x = 10
y = -5
z = 0

Floating-point variables in python

To create float variable

# Create a floating-point variable
a = 3.14
b = -2.5
c = 0.0

Boolean variables in python

To Create a boolean variable in python

# Create a boolean variable
is_python_fun = True
is_learning = False

String variables in python

To Create a string variable in python

# Create a string variable
name = "Gogo"
message = "Hello, world!"

List variables in python

To Create a list variable in python

# Create a list variable
fruits = ["apple", "banana", "orange"]
numbers = [1, 2, 3, 4, 5]

Tuple variables in python

To create tuple variable in python

# Create a tuple variable
person = ("Omar", 30, "Male")
coordinates = (3.14, -2.5)

Dictionary variables in python

To Create a dictionary variable in python

# Create a dictionary variable
person_info = {"name": "Omar", "age": 16, "gender": "Male"}

Casting in python

• In Python, casting refers to the process of converting a value from one data type to another.
• Python provides built-in functions for performing casting between different data types.

Here are some examples of casting in Python:

Casting integers to floating-point numbers in python 

# Cast an integer to a float
x = 10
y = float(x)
print(y) # Output: 10.0

Casting floating-point numbers to integers in python

# Cast a float to an integer
x = 3.14
y = int(x)
print(y) # Output: 3

Casting integers or floats to strings in python 

# Cast an integer to a string
x = 10
y = str(x)
print(y) # Output: "10"

# Cast a float to a string
x = 3.14
y = str(x)
print(y) # Output: "3.14"

Casting strings to integers or floats in python

# Cast a string to an integer
x = "10"
y = int(x)
print(y) # Output: 10

# Cast a string to a float
x = "3.14"
y = float(x)
print(y) # Output: 3.14

Casting between boolean and integer values in python

# Cast a boolean value to an integer
x = True
y = int(x)
print(y) # Output: 1

# Cast an integer to a boolean value
x = 0
y = bool(x)
print(y) # Output: False

These are some examples of casting between different data types in Python.

By using casting, you can convert values from one data type to another as needed in your program.

How to Get the Type in python?

In Python, you can use the built-in type() function to get the type of a variable or a value.

Here is an example:

# Get the type of a variable 
x = 10
print(type(x)) # Output: <class 'int'>

# Get the type of a value
y = 3.14
print(type(y)) # Output: <class 'float'>

# Get the type of a string
z = "Hello, world!"
print(type(z)) # Output: <class 'str'>

1. In this example, we use the type() function to get the type of a variable x, a value y, and a string z.
2. The output shows the type of each variable or value as a class object.
3. By using the type() function, you can check the type of any variable or value in your program.
4. This is useful when you want to make sure that the input or output of a function has the correct data type.

Single or Double Quotes  in python 

In Python, you can use either single quotes (‘…’) or double quotes (“…”) to define a string literal. Both single and double quotes work the same way and are interchangeable, so it’s a matter of personal preference which one to use.

Here are some examples:

# Using single quotes
message1 = 'Hello, world!'
print(message1) # Output: Hello, world!

# Using double quotes
message2 = "Hello, world!"
print(message2) # Output: Hello, world!

In this example:

1. we define two string variables message1 and message2 using single and double quotes, respectively.
2. Both variables contain the same string “Hello, world!” and produce the same output when printed.

There are some cases where you might need to use one type of quotes over the other.

For example, if you want to include a single quote character in a string, you should use double quotes to define the string:

# Using double quotes to include a single quote character in a string
message3 = "It's a beautiful day!"
print(message3) # Output: It's a beautiful day!

Alternatively, you can escape the single quote character using a backslash:

# Escaping the single quote character with a backslash
message4 = 'It\'s a beautiful day!'
print(message4) # Output: It's a beautiful day!

In general, it’s best to use the type of quotes that makes your code more readable and consistent with the rest of your codebase.

If you’re working on a team or contributing to an open-source project, it’s a good idea to follow the existing conventions for quoting strings.

Case-Sensitive in python 

Python is a case-sensitive language, which means that uppercase and lowercase letters are treated as distinct and separate characters.

Here’s an example to illustrate this:

# Defining two variables with different case
message1 = "Hello, world!"
message2 = "hello, world!"

# Printing the variables
print(message1) # Output: Hello, world!
print(message2) # Output: hello, world!

# Comparing the variables
print(message1 == message2) # Output: False

Python is a case-sensitive language, which means that uppercase and lowercase letters are treated as distinct and separate characters.

Here’s an example to illustrate this:

# Defining two variables with different case
message1 = "Hello, world!"
message2 = "hello, world!"
# Printing the variables
print(message1)
# Output: Hello, world!
print(message2)
# Output: hello, world!
# Comparing the variables
print(message1 == message2)
# Output: False

In this example:

1-we define two string variables message1 and message2.

2-Although the two variables contain the same characters, the second variable is written with a lowercase “h”.

3-When we print the variables, we can see that they are displayed differently because Python is case-sensitive.

4-When we compare the variables using the == operator, the result is False because the strings are not identical due to the difference in case.

It’s important to be aware of Python’s case-sensitivity when writing code to avoid errors and ensure that your code behaves as expected.

For example, if you define a variable called message with a lowercase “m”, you cannot access it using Message or MESSAGE with uppercase letters.