====== Lazy vs Eager evaluation ======

Python generally uses an eager evaluation (in contrary to [[cs_lang:haskell|Haskell]]) but for example with Python 3 the range() function returns a special range object which computes elements of the list on demand.

<code python>
>>> r = range(10)
>>> print(r)
range(0, 10)
>>> print(r[3])
3
</code>

This was not the case with Python 2 (without iterators):
<code python>
>>> r = range(10)
>>> print r
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> print r[3]
3
</code>

Lazy evaluation saves execution time for large ranges.