Variable

Variable

A place to store a value so it can be used later in code.

Variables are defined using an assignment statement.

my_number = 27  
my_number # 27  

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Before a variable is defined, it has no meaning (evaluates to None).

undefined_variable # Prints nothing, the value is None  

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Variables should have helpful, descriptive names so you know what they refer to.

Unhelpful variable names

six = 15  
i_45love_chocolate_9999 = 60 * 60 * 24 * 365  

Variable names can contain uppercase and lowercase characters, the digits 0-9, and underscores.

Helpful variable names

seconds_per_hour = 60 * 60  
hours_per_year = 24 * 365  
seconds_per_year = seconds_per_hour * hours_per_year  

They cannot start with a number.
They are case sensitive!

Invalid variable names

7_days = 24 * 7  
3 = 2 + 1  

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Some common naming conventions are UpperCamelCase for class names, CAPITALIZED_WITH_UNDERSCORES for constants, and snake_case for other names, including most variable names.