Variable Rules

 

https://www.w3schools.com/python/exercise.asp?filename=exercise_variables1

Excercise

Python Variable Names

Every Python variable should have a unique name like a, b, c. A variable name can be meaningful like color, age, name etc. There are certain rules which should be taken care while naming a Python variable:

• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number or any special character like $, (, * % etc.
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Python variable names are case-sensitive which means Name and NAME are two different variables in Python.
• Python reserved keywords cannot be used naming the variable.

Example

Following are valid Python variable names:

counter = 100
_count  = 100
name1 = "Zara"
name2 = "Nuha"
Age  = 20
zara_salary = 100000
myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"

print (counter)
print (_count)
print (name1)
print (name2)
print (Age)
print (zara_salary)

This will produce the following result:

100
100
Zara
Nuha
20
100000

Example

Following are invalid Python variable names:

1counter = 100
$_count  = 100
zara-salary = 100000

print (1counter)
print ($count)
print (zara-salary)

This will produce the following result:

File "main.py", line 3
    1counter = 100
           ^
SyntaxError: invalid syntax

P

Multi Words Variable Names

Variable names with more than one word can be difficult to read.

There are several techniques you can use to make them more readable:

Camel Case

Each word, except the first, starts with a capital letter:

myVariableName = "John"

---

Pascal Case

Each word starts with a capital letter:

MyVariableName = "John"

---

Snake Case

Each word is separated by an underscore character:

my_variable_name = "John"

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Python Variables - Assign Multiple Values

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

One Value to Multiple Variables

And you can assign the same value to multiple variables in one line:

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

Python - Output Variables

Output Variables

The Python print() function is often used to output variables.

x = "Python is awesome"
print(x)

In the print() function, you output multiple variables, separated by a comma:

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

You can also use the + operator to output multiple variables:

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

For numbers, the + character works as a mathematical operator:

x = 5
y = 10
print(x + y)

In the print() function, when you try to combine a string and a number with the + operator, Python will give you an error:

x = 5
y = "John"
print(x + y)

The best way to output multiple variables in the print() function is to separate them with commas, which even support different data types:

x = 5
y = "John"
print(x, y)

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