which is "better"?

[Skaperen]

any reason to believe one way is "better" than the other, for any definition of "better"?

    ...
    pair = ('foo','bar') # or it could be a longer tuple, always with strings
    ...
    foobar = '_'.join(('prefix',)+pair)
    foobar = 'prefix_'+('_'.join(pair))

normally i choose the code that is easier to read or the code that is shorter.  i ran into something like this, this evening, where they had the same ease to read and the same length.  maybe you have a "better" opinion.

[metulburr]

i would prefer it like this

>>> '{}{}'.format('prefix_', '_'.join(pair))
'prefix_foo_bar'

Whereas concatenating it is messy and unreadable. This way you know 2 things are being input into the string, as well as know what they 2 are by what formats parameters are.

However if i knew the tuple was always going to be two elements, i would rather do this

>>> '{}_{}_{}'.format('prefix', *pair)
'prefix_foo_bar'

[ichabod801]

The format method is generally preferred over +, from what I can find it's more efficient:

foobar = 'prefix_{}'.format('_'.join(pair))

If you know it's going to be two things, I would go for full formatting:

foobar = 'prefix_{}_{}'.format(*pair)

However, if it's a variable number, join is better.

[snippsat]

f-string in 3.6 is nice.

>>> pair = ('foo','bar')
>>> f"prefix_{'_'.join(pair)}"
'prefix_foo_bar'

[Skaperen]

it is a variable number, so join is the way, but which of the 2 i showed?

[Larz60+]

it is a variable number, so join is the way, but which of the 2 i showed?

neither -- snippsat's is best

[metulburr]

i would say neither. I am not still yet fancy to use f strings but i would say either the f-string method or format method is better than both of yours.