9.2. Operations on Strings¶

In general, you cannot perform mathematical operations on strings, even if the strings look like numbers. The following are illegal (assuming that message has type str):

message - 1
"Hello" / 123
"15" + 2

Interestingly, the + operator does work with strings, but for strings, the + operator represents concatenation, not addition. Concatenation means joining the two operands by linking them end-to-end. For example:

The output of this program is banana nut bread. The space before the word nut is part of the string and is necessary to produce the space between the concatenated strings. Take out the space and run it again.

Check your understanding

strings-3-1: What is printed by the following statements?

s: str
t: str
s = "python"
t = "rocks"
print(s + t)

python rocks
Concatenation does not automatically add a space.
python
The expression s+t is evaluated first, then the resulting string is printed.
pythonrocks
Yes, the two strings are glued end to end.
Error, you cannot add two strings together.
The + operator has different meanings depending on the operands, in this case, two strings.