Unraveling the Power of Python Variables: Your Key to Data Mastery-w9school

Discover the significance of Python variables and their role in data manipulation. Dive into Python's variable magic today!

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Python Variables

Variables serve as storage containers for various data values.

Creating Variables

In Python, there is no specific command for declaring variables.

However, when you assign a value to a variable for the first time, it is automatically created.

Example

x = 5
y = "John"
print(x)
print(y)

There is no requirement to assign a particular type to variables, and they may even alter their type after initialization.

Example

x = 4       # x is of type int
x = "Sally" # x is now of type str
print(x)

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Casting

When it comes to programming, the act of defining the data type of a variable is referred to as casting.

Example

x = str(3)    # x will be '3'
y = int(3)    # y will be 3
z = float(3)  # z will be 3.0

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Get the Type

If you need to know the data type of a variable, the type() method is a great option to consider.

Example

x = 5
y = "John"
print(type(x))
print(type(y))

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Single or Double Quotes?

You can declare string variables by using either single or double quotation marks.

Example

x = "John"
# is the same as
x = 'John'

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Case-Sensitive

It is important to pay attention to the case of variable names.

Example

This will create two variables:

a = 4
A = "Sally"
#A will not overwrite a

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Variable Names

When it comes to naming variables in Python, certain rules must be followed.

The name of a variable can be a simple one like 'x' or 'y', or a more descriptive one such as 'age', 'carname', or 'total_volume'.
The first rule is that the name must begin with a letter or underscore, and cannot start with a number. Additionally, only alphanumeric letters and underscores (A-z, 0-9, and _) are allowed.
It is important to note that the names are case sensitive, meaning that 'age', 'Age', and 'AGE' are all considered different variables.
Lastly, it is essential to avoid using Python keywords as variable names. By following these guidelines, you can confidently and efficiently name your Python variables.

Example

Legal variable names:

myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"

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Example

Illegal variable names:

2myvar = "John"
my-var = "John"
my var = "John"

Reminder: The variable names are case-sensitive.

Multi Words Variable Names

It can be challenging to comprehend variable names that have more than one word.

However, there are several methods that you can use to enhance their readability.

Camel Case

Except for the first, each word begins with a capital letter:

myVariableName = "John"

Pascal Case

Every word begins with a capital letter:

MyVariableName = "John"

Snake Case

An underscore character separates each word:

my_variable_name = "John"

The decision between a snake case or camel case is something that is a matter of personal preferences for projects. The official style guide for Python, PEP 8, recommends using snake_case to define variable and function names, and using CamelCase for names for classes. Consistency in name conventions is crucial to ensure that code is readable and maintainable.

Many Values to Multiple Variables

In Python, you can assign values to many variables in a single line:

Example

x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)

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Note: An error will occur if the number of variables doesn't match the number of values.

One Value to Multiple Variables

You can also assign the same value to numerous variables in a single line:

Example

x = y = z = "Orange"
print(x)
print(y)
print(z)

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Unpack a Collection

In Python, you can retrieve values from a list, tuple, or other collection and save them in variables, which is called unpacking.

Example

Unpack a list:

fruits = ["apple", "banana", "cherry"]
x, y, z = fruits
print(x)
print(y)
print(z)

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Output Variables

The Python print() method is commonly used to display variables.

Example

x = "Python is awesome"
print(x)

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When you need to print multiple variables, simply separate them using commas within the parentheses of the print() function. This is a straightforward way to ensure that all the desired information is displayed in one convenient location.

By following this simple guideline, you can easily print out several variables without any confusion or errors.

Example

x = "Python"
y = "is"
z = "awesome"
print(x, y, z)

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You can also output multiple variables by using the + operator:

Example

x = "Python "
y = "is "
z = "awesome"
print(x + y + z)

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Notice the space character after "Python " and "is ", without them, the result would be "Pythonisawesome".

The + character functions as a mathematical operator for numbers:

Example

x = 5
y = 10
print(x + y)

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When utilizing the + operator within the print() method in Python, it's crucial to avoid mixing a string and a number. If you do combine the two, an error will be generated. Stay mindful of this to maintain efficient and error-free programming.

Example

x = 5
y = "John"
print(x + y)

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To display multiple variables using the print() method, be sure to separate them with commas. This method is versatile and can handle a wide range of data types.

Example

x = 5
y = "John"
print(x, y)

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Global Variables

Global variables are variables that are created outside of a function, as demonstrated in all of the examples above.

These variables can be accessed by anyone, both inside and outside of functions.

Example

To utilize a variable within a function, create it outside of the function first.

x = "awesome"

def myfunc():
  print("Python is " + x)

myfunc()

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It is worth noting that when a variable is created with the same name within a function, it acquires a local scope and can only be accessed within that specific function. At the same time, the global variable with the same name will persist globally and maintain its initial value.

Example

To create a variable within a function that has the same name as a global variable, just name it the same as the global variable.

x = "awesome"

def myfunc():
  x = "fantastic"
  print("Python is " + x)

myfunc()

print("Python is " + x)

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The global Keyword

If you create a variable within a function, it's typically only accessible within that function as it's considered local. However, you can use the global keyword to declare a variable as global within a function.

For instance, if you use the global keyword, the variable belongs to the global scope.

Here's an example:

def myfunc():
  global x
  x = "fantastic"

myfunc()

print("Python is " + x)

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Also, use the global keyword if you want to change a global variable inside a function.

Example

To update the value of a global variable within a function, you can make use of the global keyword to reference the variable.

x = "awesome"

def myfunc():
  global x
  x = "fantastic"

myfunc()

print("Python is " + x)

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Test Yourself

By now, you should have a good understanding of variables and their usage in Python. Are you feeling confident and ready to apply your knowledge?

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