When does python compile the constant string letters, to combine the strings into a single constant string?

Question

such as

In [9]: dis.disassemble(compile("s = \'123\' + \'456\'", "", "exec"))
  1           0 LOAD_CONST                 


        

Answer 1

It happens whenever the combined string is 20 characters or fewer.

The optimization occurs in the peephole optimizer. See line 219 in the fold_binops_on_constants() function in Python/peephole.c: http://hg.python.org/cpython/file/cd87afe18ff8/Python/peephole.c#l149