11–20 of 28 posts
Earlier quoted context omitted.
Great catch. If you want to submit a pull request on github you can get the credit -- github.com/dcrosta/xrange
Thanks for the consideration, but I don't really use github, so you go ahead and take the credit yourself.
Nitpicking, but this statement doesn't work with large numbers (which xrange() is supposed to handle correctly): self._len = int(ceil(float(stop - start) / step)) Python supports arbitrary-length integers; you can't just cast those to (fixed-length) floating point numbers without losing precision. It's better to use integer division here, for example: self._len = (stop - start)//step + bool((stop - start)%step) (A va…
Great catch. If you want to submit a pull request on github you can get the credit -- github.com/dcrosta/xrange
However, I understand if that complaint is just too nitpicky for you to want to mention it. Great post btw.
Earlier quoted context omitted.
Huh -- CPython 2.x doesn't let you create an xrange with values past 2 63-1. CPython 3.x does.
Even 63-bit integers aren't (all) representable in IEEE double floating point values (that Python uses) which have a 53 bits mantissa. For example, int(float(10¹⁸ - 1)) != 10¹⁸ - 1, but xrange(1, 10¹⁸) is perfectly valid (even in Python 2). edit : how do I type two consecutive asterisks on Hacker News? Backslash doesn't seem to work as an escape character.
Edit: failure. That's two stymied people :(
Does anyone know how this is implemented in Pypy?
This is an excellent post and every Python hacker should read it. Kudos to the author.
Earlier quoted context omitted.
Even 63-bit integers aren't (all) representable in IEEE double floating point values (that Python uses) which have a 53 bits mantissa. For example, int(float(10¹⁸ - 1)) != 10¹⁸ - 1, but xrange(1, 10¹⁸) is perfectly valid (even in Python 2). edit : how do I type two consecutive asterisks on Hacker News? Backslash doesn't seem to work as an escape character.
\\ \\ Edit: failure. That's two stymied people :(
if len(args) == 1:
start, stop, step = 0, args[0], 1
elif len(args) == 2:
start, stop, step = args[0], args[1], 1
elif len(args) == 3:
start, stop, step = args
else:
raise TypeError('xrange() requires 1-3 int arguments')
map = [
lambda args: (0, args[0], 1),
lambda args: (args[0], args[1], 1),
lambda args: args,
]
try:
start, stop, step = map[len(args)](args)
except IndexError:
raise TypeError('xrange() requires 1-3 int arguments')
I would not do such a change to the if step block since its pattern feels noticeably different: "open" checks fit well in a if/else, whereas bunch-of-equalities fit a dispatch map better (plus you can actually modify the map at runtime).
Not worth a pull request, but personally I'd replace: if len(args) == 1: start, stop, step = 0, args[0], 1 elif len(args) == 2: start, stop, step = args[0], args[1], 1 elif len(args) == 3: start, stop, step = args else: raise TypeError('xrange() requires 1-3 int arguments') with: map = [ lambda args: (0, args[0], 1), lambda args: (args[0], args[1], 1), lambda args: args, ] try: start, stop, step = map[len(args)](args…
* Name 'map' for a variable is a poor choice (as it has same name as the python builtin function map)
* Your version has off by one error, it doesn't give correct results when called with a single element list or if the list has three elements:
>>>mymap = [
lambda args: (0, args[0], 1),
lambda args: (args[0], args[1], 1),
lambda args: args,
]
>>>args = [5]
>>>mymap[len(args)](args)
IndexError
Traceback (most recent call last)
....
# This shouldn't be the case, a list with a single
# element is a valid input
>>>args = [1,6,1]
>>>mymap[len(args)](args)
IndexError Traceback (most recent call last)
...
# This shouldn't be the case, a list with a three
# elements is a valid input