[Tutor] for loops when there is only one row in the result - is there an alternative?

[Steven D'Aprano]

Rance Hall wrote:

> Generally you have something like this:
> 
> clientlist = get_clients()  # where get_clients is a prepared sql statement.
> 
> normally you would get the individual rows like this:
> 
> for row in clientlist:
>    do stuff
> 
> 
> which is great for a long list of results.  But I'm running into
> issues when there are only 0 or 1 results in the set.

If clientlist is empty, you don't need to explicitly test for it:

 >>> clientlist = []  # nothing there
 >>> for row in clientlist:
...     print("Hello world")
...
 >>>

Notice that nothing gets printed.

> if there are zero rows then I can do something like:
> 
> if len(clientlist) == 0:
>    do stuff


Generally one merely needs to check the list itself:

if clientlist:
     ...


although be warned that "lazy lists", or iterators, are slightly 
different -- but if len(clientlist) works, then this should also work.


> I'm looking for a better way to access the row when there is just one
> row in the result.

This should work:

row, = clientlist  # if one row only -- note the comma!
row1, row2 = clientlist  # if two rows
row1, row2, row3 = clientlist  # three rows

If the comma in the first example is too subtle, try this:

[row] = clientlist

Another way which should work:

row = clientlist[0]


> Say from a user login attempt, or a request to edit an existing client record.
> 
> Is there a decent way to get direct access to the single row in the
> result set without having to go through the for loop for just one
> item?
> 
> It likely helps to know exactly what variable type clientlist would
> be.  I have no idea.

type(clientlist) will tell you.




-- 
Steven