Injection: when data becomes code

The server builds one string, "echo hello " plus the name, and gives it to a shell to run. The shell does not see a name; it sees a command line and obeys every mark in it, so a semicolon starts a second command. The crossing happens the moment the value is concatenated into the command text.

With shell=False and a list, Python runs echo directly and hands it the arguments as written. No shell is involved, so a semicolon is an ordinary character inside an argument and is printed rather than obeyed. Nothing is escaped and nothing is guessed: the value is passed as data because that is the only thing it can be.

The question mark is a placeholder. The driver sends the query text and the value separately, and the database treats the value as data, not as query text. A value such as ada OR 1=1 is then compared as a literal string and matches nothing. In the pasted version the same value closed the quote and added a condition, because it was read as code.

Encoding is a way to carry a character through a channel that would otherwise mangle it, and the server decodes it on arrival. By the time the value is concatenated into the command, the semicolon is a plain semicolon again. Encoding changes the form of a value in transit; it does not change what the value means once it has arrived.