# Function decorator exercises
####################
# Alexander Kosik

############################
# Exercise 1
############################

def double(f):
    """
    Double is a decorator which doubles the return value of passed function

    Args:
        f: function to call. Result of f should be doubled

    Returns:
        Returns a new function which calls f and doubles the result
    """
    pass # TODO


############################
# Exercise 2
############################
"""
Write a decorator function `time_this(f)` that wraps a function 
with an extra layer of logic that prints out how long it takes
for a function to execute.  To do this, you'll surround
the function with timing calls like this:
```python
start = time.time()
r = func(*args,**kwargs)
end = time.time()
print('%s.%s: %f' % (func.__module__, func.__name__, end-start))
```
Here is an example of how your decorator should work:

```python
>>> @time_this
def countdown(n):
        while n > 0:
             n -= 1

>>> countdown(10000000)
__main__.countdown : 0.076562
>>>
```

If you define a function, its name and module are stored in the
`__name__` and `__module__` attributes. For example:
```python
>>> def add(x, y):
     return x+y

>>> add.__name__
'add'
>>> add.__module__
'__main__'
>>>
```
Use the __name__ and __module__ attribute for your output
"""
def time_this(f):
    pass # TODO


############################
# Exercise 3
############################
"""
Copy your code from time_this decorator to a new decorator. 
Extend the decorator with an optional parameter `call_time=False`
which (if set to True) should print the time the function was called.

You can use datetime.now() to receive the current date and time.

For this you will need an parametrized decorator (also known as decorator
factory).
Remember: The decorator factory receives the parameters to customize the 
decorator. It must return a function which wraps and decoratores
the target function. So you need in total 3 nested functions.
"""
def time_this(call_time=False):
    def decorate(f):
        pass # TODO
    return decorate