Generator - Provide parameters to url - requests

[Peter Otten]

Sayth Renshaw wrote:

> Thanks.
> 
> I left "base" out as i was trying to remove as much uneeded code from
> example as possible. I had defined it as
> 
> base = datetime.datetime(2017,1,1)

You actually did provide that line in your post.

> Reading your code this sounds to simple :-).
> 
> def dates(first, numdays):
>     # generate datetime objects for extra clarity
>     # note there are no implicit arguments like `base` in your code
>     for _ in range(numdays):
>         yield first
>         first += ONE_DAY
> 
> Thanks

You could write the above generator

ONE_DAY = datetime.timedelta(days=1)
base = datetime.datetime(2017, 1, 1)
def dates(numdays):
    date = base
    for _ in range(numdays):
        yield date
        date += ONE_DAY

but this is bad design. 

You get the most predictable output when you write functions in such a way 
that the result only depends on the function's arguments. Such functions are 
called "pure", and are much easier to reason about and to cover with unit 
tests.

As Python does not provide constants this is sometimes a judgment call:
While ONE_DAY will never be changed base is likely to be changed to

base = datetime.datetime(2018, 1, 1)

next year. Therefore it should be an argument. If you were to change the 
generator to support varying intervals the signature should be changed, too, 
to

def dates(first, numdays, daystep=1):
    # ...

or similar.