I am new to python.
In Python, I want to sort dictionary items based on keys which is alphanumeric.

Code snippet is as follows:

```
items={'100 kg': u"apple", '500 kg': u"cabbage", '1020 kg': u"banana", '259 GB': u"carrot"}

```

I want to sort it based on their quantity in ascending order .
Is there any way to do this in Python ?

Adding ,
I sorted dictionary keys using suggested technique. After this I want to add sorted key and its corresponding value in another new dictionary so that I can get dictionary in a sorted way ,but new dictionary is not storing data as in the order that I insert.

So For that I used orderedDict of Python.

For this I am using code as:

```
import collections

items={'100 kg': u"apple", '500 kg': u"cabbage", '1020 kg': u"banana", '259 kg': u"carrot"}
sorted_keys = sorted(items, key = lambda x : int(x.split()[0]))
sorted_capacity = collections.OrderedDict()
for j in sorted_keys:
    for i in items:
        if j == i:
            print i  
            sorted_capacity[j]=items[j]
            break

```

Here I am getting error as : AttributeError: 'module' object has no attribute 'OrderedDict' 
What may be the reason for this?