85 lines
2.9 KiB
Markdown
85 lines
2.9 KiB
Markdown
---
|
|
title: The Python Range
|
|
---
|
|
## Python Ranges
|
|
|
|
Rather than being a function, a range is actually an <a href='https://docs.python.org/3/library/stdtypes.html#immutable-sequence-types' target='_blank' rel='nofollow'>immutable sequence type</a> and is commonly used for looping a specific number of times in for loops.
|
|
|
|
**Creation:**
|
|
|
|
`ranges` are created using the `range` constructor. The parameters for the constructor are:
|
|
|
|
* `start`: Inclusive first value of the range (optional integer, defaults to 0).
|
|
* `stop` : Exclusive stop value, range stops when this value or greater would be provided (required integer).
|
|
* `step` : The amount added to the current value to get the next value (optional integer, defaults to 1).
|
|
|
|
```python
|
|
>>> range(10) # Only the stop parameter is required.
|
|
range(0, 10)
|
|
>>> range(0, 10) # Default for start parameter is 0.
|
|
range(0, 10)
|
|
>>> range(0, 10, 1) # Default for step is 1\. Start parameter is required if
|
|
step is needed.
|
|
range(0, 10)
|
|
```
|
|
|
|
**Examples:**
|
|
|
|
Since `ranges` are iterables they can be passed into the `list` and `tuple` constructors to create those types of sequences. Using this fact, we can visualize some examples:
|
|
|
|
```python
|
|
>>> list(range(10)) # range as argument for list constructor.
|
|
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
|
>>> tuple(range(10)) # range as argument for tuple constructor.
|
|
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
|
|
```
|
|
|
|
Zero length `ranges`:
|
|
|
|
```python
|
|
>>> list(range(10, 0)) # start greater than stop with postive step.
|
|
[]
|
|
>>> list(range(10, 10)) # start equal to stop with postive step.
|
|
[]
|
|
>>> list(range(10, 10, -1)) # start equal to stop with negative step.
|
|
[]
|
|
>>> list(range(0, 10, -1)) # start less than stop with negative step.
|
|
[]
|
|
```
|
|
|
|
`ranges` with step arguments:
|
|
|
|
```python
|
|
>>> list(range(0, 10, 2)) # next value would be 10, stops at 8.
|
|
[0, 2, 4, 6, 8]
|
|
>>> list(range(0, 10, 3)) # next value would be 12, stops at 9.
|
|
[0, 3, 6, 9]
|
|
>>> list(range(0, 10, 4)) # next value would be 12, stops at 8.
|
|
[0, 4, 8]
|
|
>>> list(range(10, 0, -1)) # negative step makes decreasing ranges.
|
|
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
|
|
>>> list(range(-5, -30, -3)) # negative integers are valid arguments.
|
|
[-5, -8, -11, -14, -17, -20, -23, -26, -29]
|
|
```
|
|
|
|
**Benefits:**
|
|
|
|
The benefit of using `range` is that regardless of how large of a range specified, only a small amount of memory is needed to store the `range`, the values for start, stop, and step. The individual values of the `ranges` are calculated upon iteration.
|
|
|
|
```python
|
|
>>> import sys
|
|
>>> a_range = range(1000000)
|
|
>>> a_list = list(a_range)
|
|
>>> a_tuple = tuple(a_range)
|
|
>>> sys.getsizeof(a_range)
|
|
48
|
|
>>> sys.getsizeof(a_list)
|
|
9000112
|
|
>>> sys.getsizeof(a_tuple)
|
|
8000048
|
|
```
|
|
|
|
### More Inforamtion:
|
|
<a href='https://docs.python.org/3/library/stdtypes.html#ranges' target='_blank' rel='nofollow'>Python Doc - Ranges</a>
|
|
|
|
**TODO: Methods `ranges` do and do not implement** |