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Engineering LibreTexts

2.1: Values and Types

value is one of the basic things a program works with, like a letter or a number. The values we have seen so far are 12, and "Hello, World!"

These values belong to different types2 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. We use the python command to start the interpreter.

>>> print(4)

If you are not sure what type a value has, the interpreter can tell you.

>>> type('Hello, World!')
<class 'str'>
>>> type(17)
<class '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)
<class 'float'>

What about values like "17" and "3.2"? They look like numbers, but they are in quotation marks like strings.


>>> type('17')
<class 'str'>
>>> type('3.2')
<class 'str'>

They're strings.

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 comma-separated sequence of integers, which it prints with spaces between.


This is the first example we have seen of a semantic error: the code runs without producing an error message, but it doesn't do the "right" thing.