1. Q and A for Chapter 3.4 – 3.14 CS 104 Victor Norman

2. Creating new functions Q: Can you create new functions with new names, or just use the one they show in the book? A: You can create any function you want with any legal name (legal identifier, like for variables). You must define the function before calling it.

3. Creating new functions def aFunc(param1, param2): # code indented 4 spaces that does stuff print param1 + param2 def yell(param1): # param1 must be str print param1.upper() aFunc(3, 4) aFunc(“Hello”, “world”) hi = “Greetings, earthling.” yell(hi)

4. String functions Q: Why create functions that work with strings? Functions to compute math stuff are obvious. A: Lots of computing is with strings. def prependTime(outStr): # code here to get the time print time + “: “ + outStr

5. Function Parameters Q: Can functions take more than 1 or 2 parameters? A: Yes: a function definition specifies how many parameters it takes. The function call must provide that many arguments. (Reminder: a function call evaluates its arguments before calling the function, where the parameters point to those values within the function code.)

6. Functions 2 Q: Can you define a function inside a function? A: You can, but you better not until you’ve been working with python for a few years. And, besides, that inner function definition goes away when the outer function call returns, so it isn’t very useful.

7. Stack frames! Help! Q: I need help with this stack frames business. Does python actually do this? A: Python does this internally, to keep track of what code is calling what code, etc. You don’t see this when it is running. Check this out.this

8. Local Variables Q: I don’t understand local variables. A: (That’s not a question… :-) A local variable in a function is a name that refers to a value, but is created when the function code is run, and is deleted when the function returns. (A parameter is a local variable that is initialized to refer to the value passed in by the corresponding argument.)

9. References to functions Q: What happens when you call a function without ()? Like this: supposed print_twice was defined, but you “call” it this way: print_twice (without the ()) A: This is just a reference to the function print_twice. It is a reference to where the function is defined in memory. It is not a function call.

10. void functions? Q: What is the point of a void function that doesn’t return something? A: Functions that don’t return things usually: print something, or, alter some object that is passed in. So, they can be very useful.

11. from someModule import * Q: Why not always just import everything from a module? So, that you don’t have to do module.function or module.variable every time? A: You will pollute the namespace by doing it this way. But, that’s OK… for now… (We’ll talk about this much much later.)