Concatenating two range function results

Question

Does range function allows concatenation ? Like i want to make a range(30) & concatenate it with range(2000, 5002). So my concatenated range w

Answer 1

I like the most simple solutions that are possible (including efficiency). It is not always clear whether the solution is such. Anyway, the range() in Python 3 is a generator. You can wrap it to any construct that does iteration. The list() is capable of construction of a list value from any iterable. The + operator for lists does concatenation. I am using smaller values in the example:

>>> list(range(5))
[0, 1, 2, 3, 4]
>>> list(range(10, 20))
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> list(range(5)) + list(range(10,20))
[0, 1, 2, 3, 4, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

This is what range(5) + range(10, 20) exactly did in Python 2.5 -- because range() returned a list.

In Python 3, it is only useful if you really want to construct the list. Otherwise, I recommend the Lev Levitsky's solution with itertools.chain. The documentation also shows the very straightforward implementation:

def chain(*iterables):
    # chain('ABC', 'DEF') --> A B C D E F
    for it in iterables:
        for element in it:
            yield element

The solution by Inbar Rose is fine and functionally equivalent. Anyway, my +1 goes to Lev Levitsky and to his argument about using the standard libraries. From The Zen of Python...

In the face of ambiguity, refuse the temptation to guess.

#!python3
import timeit
number = 10000

t = timeit.timeit('''\
for i in itertools.chain(range(30), range(2000, 5002)):
    pass
''',
'import itertools', number=number)
print('itertools:', t/number * 1000000, 'microsec/one execution')

t = timeit.timeit('''\
for x in (i for j in (range(30), range(2000, 5002)) for i in j):
    pass
''', number=number)
print('generator expression:', t/number * 1000000, 'microsec/one execution')

In my opinion, the itertools.chain is more readable. But what really is important...

itertools: 264.4522138986938 microsec/one execution
generator expression: 785.3081048010291 microsec/one execution

... it is about 3 times faster.