Variables, Expressions, and Statement

Constants

• Fixed values such as numbers, letters, and strings, are called constants because their value does not change
• Numeric constants are as you expect
• String constants use single quotes(’) or double quotes(”)

>>> print(12)
123
>>> print(98.6)
98.6
>>> print('Hello World')
Hello World

Reserved Words

You cannot use reserved words as variable names / identifiers

Variables

• A variable is a named place in the memory where a programmer can store data and later retrieve the data using the variable “name”
• Programmers get to choose the names of the variables
• You can change the contents of a variable in a later statement

Python Variable Name Rules

• Must start with a letter or underscore _
• Must consist of letters, numbers, and underscores
• Case Sensitive

Good : spam eggs spam23 _speed

Bad : 23spam #sign var.12

Different : spam Spam SPAM

Mnemonic Variable Names

• Since we programmers are given a choice in how we choose our variable names, there is a bit of “best practice”
• We name variables to help us remember what we intend to store in them (mnemonic = “memory aid”)
• This can confuse beginning students because well-named variables often “Sound” so good that they must be keywords

Assignment Statements

• We assign a value to a variable using the assignment statement (=)
• An assignment statement consists of an expression on the right=hhand side and a variable to store the result