Chapter 2. Variables, Expressions, and Statements
Values and Types
A 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
These values belong to different types:
2 is an
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
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
because these numbers are represented in a format called floating-point.
>>> type(3.2) <type 'float'>
What about values like
'3.2'? They look like numbers, but they are in
quotation marks like strings.
>>> type('17') <type 'str'> >>> type('3.2') <type 'str'>
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:
>>> 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. 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.
One of the most powerful ...