Why does list comprehension using a zip object results in an empty list?

Question

``` f = lambda x : 2*x g = lambda x : x ** 2 h = lambda x : x ** x funcTriple = ( f, g, h ) myZip = ( zip ( funcTriple, (1, 3, 5) ) ) k = lambda pair : pair[0](pair[1]) # Why do Output # 1 (2, 9, 3125) and Output # 2 ( [ ] ) differ? print ("

Output # 1: for pair in myZip: k(pair) ...") for pair in myZip : print ( k(pair) ) print ("

Output # 2: [ k(pair) for pair in myZip ] ...") print ( [ k(pair) for pair in myZip ] ) # script output is ... # Output # 1: for pair in myZip: k(pair) ... # 2 # 9 # 3125 # # Output # 2: [ k(pair) for pair in myZip ] ... # [] ```

Accepted Answer

Works perfectly in Python 2.6 but fails in Python 3.0 because `zip` returns a generator-style object and the first loop exhausts it. Make a list instead:

```
myZip = list( zip ( funcTriple, (1, 3, 5) ) )
```

and it works in Python 3.0

Why does list comprehension using a zip object results in an empty list?

Solution

Problem