Summarize data

Please, check my code!
I forgot to include some kind of readme.st. To test custom command:
python manage.py summarize [date YYYY-MM-DD] [--nodeletion]
If you pass no parameters it summarizes current date minus 15 days (single day and no a 15-days period)
How about this
```
        try:
            datetime.strptime(processed_date, format_string)
            output = True
        except ValueError:
            output = False
        return output
```
It more clearly shows two branches and how output value is changing in each branch.