7.4. Common Function Issues¶
There are a few common mistakes you should watch out for while writing functions.
7.4.1. Returning Ends a Function¶
One common mistake when writing functions is to try to do work after a return statement.
When Python hits a return, it does just that: it returns to the place the function was
called. The program below tries to use the addFive function to add 5 to the score
only the code in that function that actually does the math comes after the return and thus
never runs! Try running it in Codelens mode to see:
Warning
A return ends a function immediately when it is hit.
7.4.2. Trying to Change a Parameter¶
The parameters for a function are variables that only exist inside of that function. You can make changes to their values, but doing so has no effect on the rest of the program.
This version of the program does not work correctly either. score is passed as the argument
from the main part of the program into addFive. That means addFive uses a copy of
score’s value as its value for x. But x and score are not actually linked. A change
to x does nothing to change the value of score. Nothing is ever returned, so the rest
of the program never learns about the changes that happened in addFive.
Again, try running in Codelens:
Warning
The only way to get information (new values) out of a function is to return them.
Check Your Understanding
The following program is supposed to convert a Celsius temp into Fahrenheight.
Put the blocks in the right order and indentation. As usual, you will not use all the blocks.