Neatest (or most readable yet still one line way) to print second tuple if first one false

Question

e.g. pictures this:

def some_operation(var) -> (bool, String):
    return False, "This is a test"


success, error_message = someOperation("aVar")
if not success:
    print(error_message)

I feel there must be a way to do something in one line that prints msg if err == false. If there were defined you could do

`success or print(error_message)`

Maybe some sort of wrapper or lambda helper to take the method call that returns the two element tuple?

`if not success: print(error_message)` can be written in one line — nikniknik2016, Mar 21 '16 at 05:09
What you have is fine. Read [this](http://stackoverflow.com/a/11880682/1832539) to help further explain. — idjaw, Mar 21 '16 at 05:10
@MitchellCurrie Your example does not include the method call either. — Selcuk, Mar 21 '16 at 05:12
Sorry, I gave the line as an example of what I'd wish to do, if it could incorporate the call too. — Mitchell Currie, Mar 21 '16 at 05:13
Readability counts. There's no need to squeeze anything into one line. — TigerhawkT3, Mar 21 '16 at 05:18
I'm calling it a lot of times in unit tests. So I guess if I wrapped it into a helper eval_method( method ) — Mitchell Currie, Mar 21 '16 at 05:18

score 2 · Accepted Answer · answered Mar 21 '16 at 05:24

2

It's best practice to use what you're using right now, but anyway, this is Python, a.k.a home of the one-liners (actually, it has second place after APL)...

(lambda success, error_message: None if success else print(error_message))(*someOperation("aVar"))

answered Mar 21 '16 at 05:24

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You're right, this is closest to what I was after although @Paul effort is good too, this squashes output if it's empty. I should more effort int the surround functions than make it one line. – Mitchell Currie Mar 21 '16 at 05:27

score 0 · Answer 2 · answered Mar 21 '16 at 05:24

Not really good practice, but this comes close to what you want:

print ''.join((not success)*message for success,message in [fn()])

To test it out:

retGood = lambda: (True, "that was good")
retBad = lambda: (False, "that was not so good")

print 'Success -> ' + ''.join((not success)*message for success,message in [retGood()])
print 'Failure -> ' + ''.join((not success)*message for success,message in [retBad()])

Prints:

Success -> 
Failure -> that was not so good

It is not quite what you asked for, as it does print a blank line if success is returned as True. But it is a one-liner to print the error message only if a False success is returned.

Interesting technique of zipping the string – Mitchell Currie Mar 21 '16 at 05:28 — Mitchell Currie, Mar 21 '16 at 05:28

Neatest (or most readable yet still one line way) to print second tuple if first one false

2 Answers2