Comprehensions in Python and Javascript are only very basic?

Question

Looking at comprehensions in Python and Javascript, so far I can't see some of the main features that I consider most powerful in comprehensions in languages like Haskell. Do they allow things like multiple generators? Or are they just a basic map-filter form? If they don't allow multiple generators, I find them quite disappointing - why have such things been left out?

Accepted Answer

Python allows multiple generators:

```
>>> [(x,y,x*y) for x in range(1,5) for y in range(1,5)]
[(1, 1, 1), (1, 2, 2), (1, 3, 3), (1, 4, 4), 
 (2, 1, 2), (2, 2, 4), (2, 3, 6), (2, 4, 8), 
 (3, 1, 3), (3, 2, 6), (3, 3, 9), (3, 4, 12),
 (4, 1, 4), (4, 2, 8), (4, 3, 12), (4, 4, 16)]
```

And also restrictions:

```
>>> [(x,y,x*y) for x in range(1,5) for y in range(1,5) if x*y > 8]
[(3, 3, 9), (3, 4, 12), (4, 3, 12), (4, 4, 16)]
```

Update: Javascript's syntax is similar (results from using the javascript shell on firefox):

```
var nums = [1, 2, 3, 21, 22, 30];
var s = eval('[[i,j] for each (i in nums) for each (j in [3,4]) if (i%2 == 0)]');
s.toSource();
[[2, 3], [2, 4], [22, 3], [22, 4], [30, 3], [30, 4]]
```

(For some reason, something about the context stuff is evaluated in in the javascript shell requires the eval indirection to have list comprehensions work. Javascript inside a `<script>` tag doesn't require that, of course)

Comprehensions in Python and Javascript are only very basic?

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