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"]:

print(i)

for name in ["Alice", "Bob", "Charlie"]:

print(name)

• Name is arbitrary –

call it whatever you

want

• i is convention for

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 7.8.1, 7.8.2, 7.10.2

ZyBooks questions

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 homework questions you'd like looked at,

for example?

Any other questions you may have?