9.8. The Accumulator Pattern with Strings¶
Strings are immutable, so they can not be changed. But it is possible
to create entirely new strings. Combining string concatenation using
+ with a loop is the accumulator pattern with strings. With it we
can create new strings from existing strings.
Remember that the accumulator pattern allows us to keep a “running total”. With strings, we are not accumulating a numeric total. Instead we are accumulating characters onto a string.
The accumulator variable, repeated_text, is intiialized on line 3
to be the empty string. Every iteration of the loop, text is
concatenated onto the end of repeated_text so it gets longer with
each iteration. Step through the function using CodeLens to see the
accumulator variable grow.
Check your understanding
- ball
- Each letter is concatenated, but the order is not correct.
- llab
- Yes, the order is reversed due to the order of the concatenation.
strings-14-1: What is printed by the following statements:
s: str
r: str
i: int
s = "ball"
r = ""
for i in range(0, len(s), 1):
r = s[i] + r
print(r)