How to make a repeating generator in Python

Question

How do you make a repeating generator, like xrange, in Python? For instance, if I do: ``` >>> m = xrange(5) >>> print list(m) >>> print list(m) ``` I get the same result both times — the numbers 0..4. However, if I try the same with yield: ``` >>> def myxrange(n): ... i = 0 ... while i < n: ... yield i ... i += 1 >>> m = myxrange(5) >>> print list(m) >>> print list(m) ``` The second time I try to iterate over m, I get nothing back — an empty list. Is there a simple way to create a repeating generator like xrange with yield, or generator comprehensions? I found a workaround on a Python tracker issue, which uses a decorator to transform a generator into an iterator. This restarts every time you start using it, even if you didn't use all the values last time through, just like xrange. I also came up with my own decorator, based on the same idea, which actually returns a generator, but one which can restart after throwing a StopIteration exception: ``` @decorator.decorator def eternal(gen…

Accepted Answer

Not directly. Part of the flexibility that allows generators to be used for implementing co-routines, resource management, etc, is that they are always one-shot. Once run, a generator cannot be re-run. You would have to create a new generator object.

However, you can create your own class which overrides `__iter__()`. It will act like a reusable generator:

```
def multigen(gen_func):
    class _multigen(object):
        def __init__(self, *args, **kwargs):
            self.__args = args
            self.__kwargs = kwargs
        def __iter__(self):
            return gen_func(*self.__args, **self.__kwargs)
    return _multigen

@multigen
def myxrange(n):
   i = 0
   while i < n:
     yield i
     i += 1
m = myxrange(5)
print list(m)
print list(m)
```

How to make a repeating generator in Python

Solution

Problem