Lessons · Python · strings cannot be changed

Text cannot be changed, only replaced

String methods hand back a NEW string. The original is never altered.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

Cleaning up what a person typed is constant work: trimming spaces, fixing case, removing characters. If you forget to catch the result, nothing appears to happen and the bug is invisible.

How to think about it

Ask: did I CATCH what that gave me? If a line calls a string method and does not assign or use the result, that line does nothing at all.

Worked example

name = "  Ada  "

With spaces a person accidentally typed.

name.strip()

Produces "Ada" and throws it away. name is unchanged. This line accomplishes nothing.

name = name.strip()

Catches the new string. Now name is "Ada".

print(name.upper())

Prints ADA, and name itself is still "Ada".

Your turn

Store the lowercase version of a name.

name = "ADA"
name = name.()
print(name)

The trap

Writing name.strip() on its own and expecting name to change. It is the most common silent no-op in Python, and nothing warns you.

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