while_ two variables, third at type should be the same.
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2. Variables, expressions and statements
2.1. Values and data types
A value is one of the fundamental things — like a letter or a number — that a program manipulates. The values we have seen so far are 2 (the result when we added 1 + 1), and "Hello, World!".
These values belong to different data types: 2 is an integer, and "Hello, World!" is a string, so-called because it contains a string of letters. You (and the interpreter) can identify strings because they are enclosed in quotation marks.
The print statement also works for integers.
>>> print 4
4
If you are not sure what type a value has, the interpreter can tell you.
>>> type("Hello, World!")
<type 'str'>
>>> type(17)
<type 'int'>
Not surprisingly, strings belong to the type str and integers belong to the type int. Less obviously, numbers with a decimal point belong to a type called float, because these numbers are represented in a format called floating-point.
>>> type(3.2)
<type 'float'>
What about values like "17" and "3.2"? They look like numbers, but they are in quotation marks like strings.
>>> type("17")
<type 'str'>
>>> type("3.2")
<type 'str'>
They’re strings.
Strings in Python can be enclosed in either single quotes (‘) or double quotes (”):
>>> type('This is a string.')
<type 'str'>
>>> type("And so is this.")
<type 'str'>
Double quoted strings can contain single quotes inside them, as in "Bruce's beard", and single quoted strings can have double quotes inside them, as in 'The knights who say "Ni!"'.
When you type a large integer, you might be tempted to use commas between groups of three digits, as in 1,000,000. This is not a legal integer in Python, but it is legal:
>>> print 1,000,000
1 0 0
Well, that’s not what we expected at all! Python interprets 1,000,000 as a list of three items to be printed. So remember not to put commas in your integers.
2.2. Variables
One of the most powerful features of a programming language is the ability to manipulate variables. A variable is a name that refers to a value.
The assignment statement creates new variables and gives them values:
>>> message = "What's up, Doc?"
>>> n = 17
>>> pi = 3.14159
This example makes three assignments. The first assigns the string "What's up, Doc?" to a new variable named message. The second gives the integer 17 to n, and the third gives the floating-point number 3.14159 to pi.
The assignment operator, =, should not be confused with an equals sign (even though it uses the same character). Assignment operators link a name, on the left hand side of the operator, with a value, on the right hand side. This is why you will get an error if you enter:
>>> 17 = n
A common way to represent variables on paper is to write the name with an arrow pointing to the variable’s value. This kind of figure is called a state diagram because it shows what state each of the variables is in (think of it as the variable’s state of mind). This diagram shows the result of the assignment statements: