Python enumerate and zip

# Python enumerate and zip Built-in Functions

`enumerate()` and `zip()` are built-in functions that can be used on sequences.

## enumerate()

The `enumerate()` function can be use to iterate over indices and items of a list.

Here's an example using a for loop to print the index (i) and value (v).

```python
>>> a = ["a", "b", "c"]
>>> for i, v in enumerate(a):
        print i, v
0 a
1 b
2 c
```

## zip()

The `zip()` function can be used to iterate over two or more lists in parallel.

```python
>>> a = [1, 2, 3]
>>> b = [3, 4, 5]
>>> c = [6, 7, 8]
>>> for i, j, k in zip(a, b, c):
        print i, j, k
1 3 6
2 4 7
3 5 8
```

### Use zip() and enumerate() together

Here is how to iterate over two lists and their indices using `enumerate()`
together with `zip()`.

```python
>>> alist = ['a1', 'a2', 'a3']
>>> blist = ['b1', 'b2', 'b3']
>>>
>>> for i, (a, b) in enumerate(zip(alist, blist)):
        print i, a, b
0 a1 b1
1 a2 b2
2 a3 b3
```

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**References**

- [How to use Python's enumerate and zip to iterate over two lists and their indices](http://www.saltycrane.com/blog/2008/04/how-to-use-pythons-enumerate-and-zip-to/)
- [Python enumerate() and zip() built in functions](http://editdistance.com/python-enumerate-and-zip-built-in-functions/)