6.3.4 Creating a list of integers
The range
command creates lists of equally spaced numbers.
It can take one, two or three arguments.
-
With one argument, range takes n, a positive integer.
- range(n) returns the list [0,1,…,n−1].
- Alternatively, range takes two mandatory and one optional argument:
-
a and b, two real numbers with a<b (unless the third
argument p is provided and negative).
- Optionally, p, a nonzero real number used for the step size (by
default 1). If p<0, then a must be larger than b.
- range(a,b ⟨,p ⟩) returns the list
[a,a+p,…] up to, but not including, b.
Examples
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| ⎡
⎣ | 2.3,3.3,4.3,5.3,6.3,7.3 | ⎤
⎦ |
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|
You can use the range command to create a list of values
f(k), where k is an integer satisfying a certain condition. (See
Section 25.3.3 for the for loop used below.)
You can list the values of an expression in a variable which
goes over a range defined by range. For example:
| [k^2+k for k in range(10)] |
|
| |
| ⎡
⎣ | 0,2,6,12,20,30,42,56,72,90 | ⎤
⎦ |
| | | | | | | | | | |
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You can list the values of an expression in a variable which
goes over a range defined by range and which satisfies a
given condition. For example:
| [k for k in range(4,10) if isprime(k)] |
(See Section 7.1.14 for isprime.)
| [k^2+k for k in range(1,10,2) if isprime(k)] |