implicitly concats of adjacent strings does not work with format

Dave Angel davea at davea.name
Wed Apr 29 15:14:59 CEST 2015


On 04/29/2015 08:42 AM, Cecil Westerhof wrote:
> I have the folowing print statements:
>      print(
>          'Calculating fibonacci_old, fibonacci_memoize and '
>          'fibonacci_memoize once for {0} '.format(large_fibonacci))
>
>
>      print(
>          'Calculating fibonacci_old, fibonacci_memoize and '
>          'fibonacci_memoize once for {0} '.format(large_fibonacci) +
>          'to determine speed increase')
>
>      print(
>          'Calculating fibonacci_old, fibonacci_memoize and '
>          'to determine speed increase'
>          'fibonacci_memoize once for {0} '.format(large_fibonacci))
>
>
>      print(
>          'Calculating fibonacci_old, fibonacci_memoize and '
>          'fibonacci_memoize once for {0} '.format(large_fibonacci)
>          'to determine speed increase')
>
> The first three work, but the last gives:
>          'to determine speed increase')
>                                      ^
>      SyntaxError: invalid syntax
>
> Not very important, because I can use the second one, but I was just
> wondering why it goes wrong.
>

Adjacent string literals are concatenated.  But once you've called a 
method (.format()) on that literal, you now have an expression, not a 
string literal.

You could either change the last line to

          + 'to determine speed increase')

or you could concatenate all the strings before calling the format method:


     print(
         'Calculating fibonacci_old, fibonacci_memoize and '
         'fibonacci_memoize once for {0} '
         'to determine speed increase' .format(large_fibonacci))

Something you may not realize is that the addjacent-concatenation occurs 
at compile time, so your third example could be transformed from:

     print(
         'Calculating fibonacci_old, fibonacci_memoize and '
         'to determine speed increase'
         'fibonacci_memoize once for {0} '.format(large_fibonacci))

to:
     print(
         'Calculating fibonacci_old, fibonacci_memoize and '
         'to determine speed increase'
         'fibonacci_memoize once for {0}'
         ' '.format(large_fibonacci))


All three literals are combined before format() is called.  Knowing this 
could be vital if you had {} elsewhere in the 9single) literal.

-- 
DaveA



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