CS 105 SUMMER WEDNESDAY 5 Hey Max, what about that bee movie - PowerPoint PPT Presentation

CS 105 SUMMER – WEDNESDAY 5

Hey Max, what about that bee movie thing? patient!  Jokes aside – still intend to  Probably Week 6, 7, or 8, as we'll have time  May have to be email - SMS apis are pricier than they used to be

What to talk about today?  From the muddiest points  While loop vs For loop  Loop nesting – when, why, etc (ZyBooks 7.8.1, 7.8.2, 7.10.2)  Why care about dynamic typing?  What's with global vs local? When does it matter?  Your questions – please feel free to post questions you'd like to see in chat!

Quick MPs  In the context of for loops - "Do you have to define i before using it? Also, does the loop variable have to be i or it could be any variable? " for i in ["Alice", "Bob", "Charlie"]: • Name is arbitrary – print(i) call it whatever you want for name in ["Alice", "Bob", "Charlie"]: • i is convention for print(name) index

Quick MPs  Some MPs:  " I also struggle on some parts of the homework."  "Can we have quiz review sessions?"  Please post your questions to Piazza. Also use office hours/tutoring!! (should have better hours…)  Piazza exists for a dialog – it's okay if what you have is a broken code and a "yo wtf?!"

Quick MPs  “confused about why range(0,5) doesn't go until 5 is that just something that i should know and accept or is there like an actual reason”  Largely something you should just accept, but there is a good reason  Think looping through list indices (without enumerate)  range(len(my_list)) – > 0 up to the last index of the list  if my_list is [1,2,3,4], then range(4) gives me (0,1,2,3)  In brief – exclude the end so you can use the length as the stopping point  Same idea with slicing to the end

Quick MPs  "Could we go deeper into polymorphism?"  We could …largely out of class scope for the summer  Polymorphism is a key part of object-oriented languages (like Python, Java)  Plan to talk about in optional video content/maybe optional parts of class meeting in Week 8

Quick MPs  "Why do docstrings matter?"  From Python.org:  A docstring is a string literal that occurs as the first statement in a module, function, class, or method definition. Such a docstring becomes the __doc__ special attribute of that object.  Basically, a fancy comment telling you WHAT a function does  Good habit for larger programming projects, but not really a part of this course

Quick MPs  "When I'm taking a quiz or the final and there's a question that I am unsure of, what are the first things I should think or look for that would help me find the right solution to the problem?" 1. Question prompt 2. Python docs 3. Trying anything in Repl.it

For example – area code from a phone number  Identifies a technique – slicing  Also gives a worse cast test case – could try return '555' if all else fails

So…slicing…docs are weird

So…slicing…docs are weird

So…slicing…docs are weird

Quiz 4 comments  High level stats: Mean 84%, Median 88%  Good job! Trending up!!  …Is stonks still funny?  Was it ever funny?

Practice Quiz 5  Slightly different question setup  Still 30, but 5 programming Qs  Excel as much as HW7 – lab solutions posted to help with this!  Looking at doing a code reading question on Quiz 6, Quiz 7

While loop vs For loop  High level –  while loop is "indefinite" -> runs until a condition ends  for loop can also be considered a "for each loop" -> "for each item in this thing"  The thing can be:  a list (or other collection)  a range statement  etc.

Can for loops and while loops do the exact same things?  In a manner of speaking…  For example, we could make an infinite for loop  Note this loop isn't really "running until X condition", though for element in my_list: my_list.append(new_element) #This won't actually #extend the loop!

Better to think about what each loop is BEST for  for loops – looping over collections, processing each element of SOME THING, "x" number of steps  while loops – Running until a sentinel value, running until something is true or something else is no longer true

break and continue – best with while  Let's code this:  "Write a program which gets a list of numbers from the user. If the user enters a non-numeric string, skip the string. If the user enters a negative number, end and print the list"  We will need str.isnumeric() for this

Did we need break?  No – we used break to break the while True, but could have also just used a sentinel value  continue here was also not strictly needed, but simplified it down from an else  You almost never STRICTLY NEED continue or break UNLESS you have an otherwise infinite loop (while True: )

Using break with for loops – decent example  Let's write this function…  "Write a function that takes a list of numbers as an argument. Sum up all the numbers up to the first negative number and return that sum"

ZyBooks questions ZyBooks 7.8.1, 7.8.2, 7.10.2

Dynamic typing, global vs local  Largely, these are concerns you'd only deal with in larger pieces of code, outside of the course scope  Dynamic is still a little bit neat  We can use type-checking to take advantage of dynamic typing…

An example of dynamic typing being useful  Let's write a function which can take either a string or a list.  If it's a list, return the sum of all the numbers in that list  If it's a string, split it on commas (,) and return the sum of all the numbers in that string  Assume we'll either get a list of numbers or a csv string

Global vs local  Largely, everything you've been writing is local  Why is global bad? Changing a variable by accident (dynamic typing negative!!)  Avoiding globals – principle for larger programs  Still sometimes useful, like importing the math module globally

Any other questions you may have? Any homework questions you'd like looked at, for example?