Difference between yield in Python and yield in C#

Question

What is the difference between yield keyword in Python and yield keyword in C#?

Answer 1

The most important difference is that python yield gives you an iterator, once it is fully iterated that's over.

But C# yield return gives you an iterator "factory", which you can pass it around and uses it in multiple places of your code without concerning whether it has been "looped" once before.

Take this example in python:

In [235]: def func1():
   .....:     for i in xrange(3):
   .....:         yield i
   .....:

In [236]: x1 = func1()

In [237]: for k in x1:
   .....:     print k
   .....:
0
1
2

In [238]: for k in x1:
   .....:     print k
   .....:

In [239]:

And in C#:

class Program
{
    static IEnumerable Func1()
    {
        for (int i = 0; i < 3; i++)
            yield return i;
    }

    static void Main(string[] args)
    {
        var x1 = Func1();
        foreach (int k in x1) 
            Console.WriteLine(k);

        foreach (int k in x1)
            Console.WriteLine(k);
    }
}

That gives you:

0
1
2
0
1
2