5.3. Range

5.3.1. Rationale

  • Return sequence of numbers

  • It is not a generator

  • Generator (lazy evaluated)

  • Built-in

5.3.2. Syntax

  • range([start], <stop>, [step])

  • optional start, inclusive, default: 0

  • required stop, exclusive,

  • optional step, default: 1

5.3.3. Problem

>>> i = 0
>>> result = []
>>> while i < 3:
...     result.append(i)
...     i += 1
>>>
>>> result
[0, 1, 2]

5.3.4. Solution

>>> result = range(0,3)
>>> list(result)
[0, 1, 2]

5.3.5. Lazy Evaluation

>>> for i in range(0,3):
...     print(i)
0
1
2

5.3.6. Use Cases

>>> list(range(0,3))
[0, 1, 2]
>>> tuple(range(0,3))
(0, 1, 2)
>>> set(range(0,3))
{0, 1, 2}
>>> list(range(4,11,2))
[4, 6, 8, 10]

5.3.7. Itertools

>>> from itertools import count
>>>
>>>
>>> result = count(3, 2)
>>>
>>> next(result)
3
>>> next(result)
5
>>> next(result)
7

5.3.8. Assignments

Code 5.55. Solution
"""
* Assignment: Designaptterns Idiom Range
* Filename: designpatterns_idioms_range.py
* Complexity: medium
* Lines of code: 25 lines
* Time: 21 min

English:
    1. Use data from "Given" section (see below)
    2. Define class `Range` with parameters: `start`, `stop`, `step`
    3. Write own implementation of a built-in `range(start, stop, step)` function
    4. How to implement passing only stop argument (`range(start=0, stop=???, step=1)`)?
    5. All tests must pass
    6. Compare result with "Tests" section (see below)

Polish:
    1. Użyj danych z sekcji "Given" (patrz poniżej)
    2. Zdefiniuj klasę `Range` z parametrami: `start`, `stop`, `step`
    3. Zaimplementuj własne rozwiązanie wbudowanej funkcji `range(start, stop, step)`
    4. Jak zaimplementować możliwość podawania tylko końca (`range(start=0, stop=???, step=1)`)?
    5. Wszystkie testy muszą przejść
    6. Porównaj wyniki z sekcją "Tests" (patrz poniżej)

Hint:
    * use `*args`
    * `if len(args) == ...`

Tests:
    >>> from inspect import isclass, ismethod
    >>> assert isclass(Range)

    >>> r = Range(0, 0, 0)
    >>> assert hasattr(r, '__iter__')
    >>> assert hasattr(r, '__next__')
    >>> assert ismethod(r.__iter__)
    >>> assert ismethod(r.__next__)

    >>> list(Range(0, 10, 2))
    [0, 2, 4, 6, 8]

    >>> list(Range(0, 5))
    [0, 1, 2, 3, 4]

    >>> list(Range(5))
    [0, 1, 2, 3, 4]

    >>> list(Range())
    Traceback (most recent call last):
    ValueError: Invalid arguments

    >>> list(Range(1,2,3,4))
    Traceback (most recent call last):
    ValueError: Invalid arguments

    >>> Range(stop=2)
    Traceback (most recent call last):
    TypeError: Range() takes no keyword arguments

    >>> Range(start=1, stop=2)
    Traceback (most recent call last):
    TypeError: Range() takes no keyword arguments

    >>> Range(start=1, stop=2, step=2)
    Traceback (most recent call last):
    TypeError: Range() takes no keyword arguments
"""