`md5()` requires a string or buffer:

```python
>>> hashlib.md5(sorted({"foo": 1}.items()))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must be string or buffer, not list

>>> hashlib.md5(repr(sorted({"foo": 1}.items())))
<md5 HASH object @ 0x10d122d70>
```