Iterating in a closed range [a, b] in python

Question

I want to iterate over a closed range of integers [a, b] in python, ie. iterating from a to b including both a and b.

I know the following way of doing it:

for i in range(a, b+1):
    do_something(i)

For iterating in the reverse direction (ie. in the order b, b-1, b-2, ..., a), I do the following:

for i in range(b, a-1, -1):
    do_something(i)

I don't like this addition (b+1 in the example) and subtraction (a-1 in the example) to reach the closed end of the range. I find it less readable than the c/c++/Java counterpart (usage of <= in a loop).

Do you have something in python which can be used to iterate between the closed ranges without manual intervention of the boundaries?

Dc

Why do you need this? Actual sequential integers are very rarely needed. Most of the time you are iterating over iterators (in Java/C++ as well). – Bronchoscope

As long as you remember that the end parameter is exclusive (corresponding to < or > in a for loop), you won't have any trouble adjusting to it. Another way to think about it is that range(a,x)+range(x,b) = range(a,b), which wouldn't be the case if it was inclusive with respect to the end parameter. – Notification

You can define your own range() function modifying these to achieve this. – Ruffina

@PavelAnossov, I met with this situation a lot of time when I have an actual need of iterating over a range. – Dc

@AshwiniChaudhary, So no standard, ready to use functions/methodologies like that in python? – Dc

@Dc AFAIK there are no such range functions in python, similar question: #4505162 – Ruffina

@krips89: I was hoping for an actual example. – Bronchoscope

Answer 1

It's a simple matter to define your own function and use it:

def closed_range(start, stop, step=1):
  dir = 1 if (step > 0) else -1
  return range(start, stop + dir, step):

In action:

>>> list(closed_range(1, 10))
0: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> list(closed_range(1, 10, 2))
1: [1, 3, 5, 7, 9]
>>> list(closed_range(1, 10, 3))
2: [1, 4, 7, 10]
>>> list(closed_range(10, 1, -1))
3: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> list(closed_range(10, 1, -2))
4: [10, 8, 6, 4, 2]

Save to a .py file in \PythonXX\Lib\site-packages and then you can import it for use elsewhere.

Matazzoni

Yeah its simple to write some function like that, but I was looking if something was available in the python library itself and if not why they thought it was unnecessary. – Dc