Concatenating immutable strings always results in a new
object. This means that building up a string by
repeated concatenation will have a quadratic runtime cost in
the total string length.
To get a linear runtime cost,
you must switch to one of the alternatives below:
if concatenating bytes objects, you can similarly use
bytes.join(), or you can do in-place
concatenation with a bytearray object. bytearray objects are mutable and have an
efficient overallocation mechanism.