CS50 2021 in HDR - Lecture 6 - Python

This is CS50, Harvard University's Introduction to the intellectual enterprises of computer science and the art of programming. Enroll for free at cs50.edx.org/. Slides, source code, and more at cs50.harvard.edu/x. Playlist at • CS50 Lectures 2021 (HDR) .
TABLE OF CONTENTS
00:00:00 - Introduction
00:01:17 - Python
00:03:42 - Syntax
00:18:19 - Types
00:20:48 - CS50 Library
00:22:55 - Compilation and Interpretation
00:26:55 - blur.py
00:33:00 - dictionary.py
00:45:17 - hello.py
00:49:57 - calculator.py
00:55:25 - Exceptions
01:00:49 - Floating Point Imprecision
01:02:17 - points.py
01:05:49 - agree.py
01:13:00 - meow.py
01:21:44 - mario.py
01:38:23 - Documentation
01:41:45 - scores.py
01:45:59 - uppercase.py
01:49:56 - Command-line Arguments
01:54:10 - Exit Status
01:56:34 - numbers.py
01:57:40 - names.py
01:58:49 - Dictionaries
02:05:33 - CSV Files
02:16:20 - Speech Synthesis
02:18:04 - Facial Recognition
02:20:53 - Speech Recognition
02:22:31 - QR Codes
02:23:46 - This was CS50
***
This is CS50, Harvard University's introduction to the intellectual enterprises of computer science and the art of programming.
***
HOW TO SUBSCRIBE
kzbin.info_c...
HOW TO TAKE CS50
edX: cs50.edx.org/
Harvard Extension School: cs50.harvard.edu/extension
Harvard Summer School: cs50.harvard.edu/summer
OpenCourseWare: cs50.harvard.edu/x
HOW TO JOIN CS50 COMMUNITIES
Discord: / discord
Ed: cs50.harvard.edu/x/ed
Facebook Group: / cs50
Faceboook Page: / cs50
GitHub: github.com/cs50
Gitter: gitter.im/cs50/x
Instagram: / cs50
LinkedIn Group: / 7437240
LinkedIn Page: / cs50
Medium: / cs50
Quora: www.quora.com/topic/CS50
Reddit: / cs50
Slack: cs50.edx.org/slack
Snapchat: / cs50
SoundCloud: / cs50
Stack Exchange: cs50.stackexchange.com/
TikTok: / cs50
Twitter: / cs50
KZbin: / cs50
HOW TO FOLLOW DAVID J. MALAN
Facebook: / dmalan
GitHub: github.com/dmalan
Instagram: / davidjmalan
LinkedIn: / malan
Quora: www.quora.com/profile/David-J...
TikTok: / davidjmalan
Twitter: / davidjmalan
***
CS50 SHOP
cs50.harvardshop.com/
***
LICENSE
CC BY-NC-SA 4.0
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License
creativecommons.org/licenses/...
David J. Malan
cs.harvard.edu/malan
[e-mail]

[@JarodColdbreak]

1:12:48 "There are no pointers in Python." Mr. Malan please I can only handle so much pleasure at a time.

[@bobert6644]

Same 😭. My brain still hurts from week 5

[@abdulmajeedyasan5829]

ikr 😂😂😂😂

[@Pantherrrr]

David: "This is definitely coming out of the video." Me, 3 months later: "That's what you think, buddy."

[@khairm]

Any idea if they found out what happened?

[@Lark703]

@@khairm Yeah i was wondering this too. I was actually following along with David in VScode during the lecture and I also ran into the same bug. Still not sure why it was doing that

[@NodeLedge]

I think he forgot to compile the new code before running it. He deleted the old phonebook code he had and then he wrote knew code on top of it and forgot to compile it.

[@KarlDag]

@@NodeLedge python is an interpreted language, not compiled. But he might have forgotten to save the new code, that I agree.

[@jordanchen23]

Anybody else feel proud of the fact that they've done the harder thing by starting in the deep end with C and now find the idea of something like python to be convenient but "lazy"? Sort of like learning about the dish washer when you've been doing dishes by hand your whole life without issue.

[@coding3438]

2:03:47 ''This is gonna get deleted from the video" editor : aint gonna happen!

[@JesseLeeHumphry]

2:19:35 "I would have to look this up to write it again" Thank you *so much* for saying that. This consistent validation of the imperfection of the human at the keyboard is so reassuring and makes me feel way less dumb for not knowing things right off-hand.

[@jlpeng9036]

same haha

[@hschnabel3055]

When I started my last job one and a half years ago I started a glossary just to help me remember. It's got like 2k ints now... Still growing. I guess my memory is broken. You there, mallog? 😅

[@RakibulIslam-yz3gn]

I noticed that too. A great teacher who constantly reminds you - "you are not dumb".

[@CaptWindShear]

The QR code thing at the end was fantastic. So simple!

[@rQ816]

Throughout this lecture, I kept thinking 'this is too much too fast'. After this video though, I found myself reading a Python course book like a comic book, like 100 pages in 15 minutes. I am so grateful 🙏

[@cynthiabutler2529]

What's the name of the book?

[@ignaciomunoz7621]

Care to share the name of the book? Please, I'm also interested :)

[@bikdigdaddy]

@@ignaciomunoz7621 y'all can start 'learn python 3 the hard way' or 'python crash course', both are amazing

[@OfficialSombrero]

@@ignaciomunoz7621 There is a ton of other courses and books available online if you look. Don't worry about that specific one.

[@danivanon]

Which book?

[@Aliocantinea]

2:03:11 I am glad you kept this bug in, it was nice to see what someone familiar with command line can do quickly to move around and that mistakes happen all the time I am really enjoy this class so far and so happy to finally be on python!!

[@mon0theist_tv]

Does anyone know what the problem was?

[@Aliocantinea]

@@mon0theist_tv not really, you can hear someone trying to explain but I can't make out the words

[@andrewhorton95]

@@mon0theist_tv I'm wondering if it has to do with the CLI slip-up at 1:58:16, since that's where he's writing the program that's supposed to return "found."

[@GroupRoblox]

Even though I’ve already learned python through a course and self learning, I still find this lecture a masterpiece.

[@learningstuff8288]

I know right!

[@kwanjustin]

If you look at the light bulbs at the front of the stage, each lecture has a different sequence. They represent a sequence of binary that translates to different messages! For example, in this lecture, 01101000 01100101 01101100 01101100 01101111 00101110 01110000 01111001 translates to "hello.py"

[@hafizabdulmanan2989]

How you actually find it :) hahahhaha

[@kwanjustin]

@@hafizabdulmanan2989 I just noticed that they were there every single lecture, so I thought they must have some meaning

[@sarithasalian6958]

:O

[@bekzotadylov3221]

I knew that they had a meaning :D

[@arthur_p_dent4282]

hahaha! I was actually wondering that starting back at the first lecture and than filed it in the back of my brain and forgot about it.

[@djallel6471]

Never thaught i'll get rick roolled by David, Great lecture as always

[@alexissomethingrose]

Ouch, spoiler alert 😂😂

[@djallel6471]

@@alexissomethingrose sorry if i spoiled it for you 😅

[@alexissomethingrose]

@@djallel6471 naah, that’s all right! 🙏🏼😂 These lectures are next level 😎

[@Pantherrrr]

This is the first time I read the comments before watching the lecture. Kinda wish I didn't now, haha.

[@marvinmoltgen7349]

I have read this comment half way through the lecture. Got rick rolled watched further, now without the fear and then got rick rolled again 🤯 Stay save folks

[@MrX-nc8cm]

This was magnific! I can't think of another course that condences a complete programing lenguage in one video. Best course ever!

[@vahsek7488]

Have a big respect and support for you from India🇮🇳🇮🇳

[@sayori3939]

I have a warning about the lab 6: There will be a "simulate_tournament" function, be sure to return a string containing the name of the team instead of the dictionary, because even if you process it correctly and the program work fine the cs50 check will complain

[@brunorocha9898]

just amazing this series of videos. Thank you so much, I'm learning a lot.

[@chairisamira4576]

We are lucky to have this folks !! If the pace is too fast for you though , check the 2020 course version. I find the explanations slower and more digestable.

[@sentient_strong_spiritual]

I love David Malan. The best teacher in the whole world. Thank you so much for this cource!

[@Blezerker]

Going from C to Python, and seeing how EASY everything is honestly just leaves me baffled. Makes me feel like the sky is the limit!

[@lonerkid5550]

Can't believe the professor Rick Rolled us!! Fun and informative lectures.😁

[@Tarakiiht]

I am a fan of you @david, the way you have explained the python that was amazing

[@davidjmalan]

Thank you!

[@adrinuk_gamedev]

I really love this course :,)

[@HHJoshHH]

David is an awesome Prof! Fantastic lecture!

[@ismaildincer259]

2:02:36 same thing happened to me. Thank god you included this part into the video. If you didn't I would freak out.

[@ovbous]

Thank you for this great lecture :)

[@MyatMinSoe]

The whole lecture is actually David flexing python.

[@hammadhafeez4224]

This is exactly what I needed to hear!!!!🤟🇵🇰

[@muzaffarsabitjanov3843]

Thank you so much, for your work!

[@chootybeeks1088]

I literally yelled "WHAT" when he went through blur.py. that code in C made me want to cry

[@sayori3939]

Yeah and i forgot to set nice names to the "directions" of "nearby" indexes

[@v4st32]

Thank you for recent uploads!

[@Bellpepper402]

I am so glad I suffered through that speller hell nightmare because only this way would I appreciate python the way I do now.

[@sayori3939]

Hehehe true unfortunately i had to cheat because i was getting a weird seg fault, ( i actually don't feel bad about cheating because the problem was at the unload function, but when i was testing, it wouldn't "reach" print in the first line of unload, so all the time i thought the problem was in check/load, and i was already starting to hate c since week 3's cash problem)

[@illusorymoires2138]

these lectures are kind of all over the place. i keep having issues with cant join int / str… is that bc im not using the get_int library?

[@DivitKalem]

Another amazing lecture. Thanks a lot and respects to Master David. I have a question: 38:53 Is'nt the process expected to be faster if we create a hash table (as we did in C) instead of adding all 140K words in the dictionary to a set? I tried, but it got even slower. 😅

[@cameronsmith7990]

Oh Python, how I’ve missed you 😭💕

[@andrewsodyssey5753]

This helped a ton

[@lockelamora]

2:03:28 debugging in a nutshell

[@user-xq6cl2si2e]

Let's go fellas! We got this

[@MitchellRoman97]

Silly question because I could just try this myself but I’m curious, at 1:29:15, on line 8, could just adding “.int” to the end accomplish the same as adding “int” to the beginning like he did? Thanks!

[@Valyssi]

No because that would require for strings to have a .int method. Methods and 'regular' functions are entirely distinct, methods have to be defined "on the object or class" (which I believe is covered in more detail later in the course, along with when it is best to define a method over a regular function). The function int however is defined globally and cannot be used as a method.

[@adrianabiazzoto1064]

@@Valyssi Great comment! Thank you for the explanation

[@bsykesbeats4013]

2:02:35 does anybody know what happened there???.... I had the same problem happen to me, after I accidentally tried to compile a .py out of habit, using make, then when I tried to run that program, it kept running a different program, until I did the same temporary fix he did, by moving the program to a temp folder... Any insight??

[@josepayne1390]

VSCode bug I assume

[@Pabloskatepk92]

great content. I wish KZbin were like this always.

[@tommyv4980]

What are you talking about? KZbin is literally filled with tutorials and lessons...

[@sayori3939]

@@tommyv4980 yeah, and that has nothing to do with KZbin, just the people who actually record the videos ._.

[@jankarlbinarao2604]

I felt rick-rolled after spending hours in problem set 1 to 5 in c, when David has shown how to do it in python. Befits the ending of this class.

[@ninjaboy191]

This is the only lecture where I feel we went too fast and I don't know "why" we are doing certain things. Like using main to create abstraction for meow. Why when we can use the two line version? Or Mario with the break then return n vs the simple break. I get it sort of but for the first time it's not natural to do so.

[@elsupergamersuper]

Maybe I'm a bit late - I think he's trying things multiple ways for the sake of demonstration. For example, the 'meow' program isn't very useful by itself and, considering how small it is, it definitely isn't mandatory to abstract functions there. However, in larger programs, you will have to use abstractions to keep it readable, and that's why he does it with the meow: so you can see how it works in a small, simple program.

[@solaris413]

thank u so much

[@vmarcelo49]

did you guys found out what happened in 2:03:27 ???

[@ryanlee5558]

Not from me but from the CS50 discord: If you have a file called numbers.py in the same folder as dictionary.py, rename numbers.py to something else The error occurs because something in the CS50 library tries to use the built in numbers library but it will first look locally and think that your numbers.py is the library and runs it (which is why in this case it prints out "Found" because Prof David created a file called numbers.py to do that earlier) When import is used in python, it looks in the local folder first for the libraries

[@MrX-nc8cm]

@@ryanlee5558 Thanks, you saved us a head ache

[@sayori3939]

Oh yeah guys be careful on your file names, for example don't name the file the same name as a library your using, it will complain

[@TariqYasiinProd]

I never imagined in my life that I would get Rick-Rolled by a teacher lol

[@arvinmistry9744]

David please can you able to tell me how I can install cs50 libraries in Linux termux .

[@alexren9200]

first, you need install pip,like I use archlinux, sudo pacman -S python-pip,then pip3 install cs50

[@davidjmalan]

See cs50.readthedocs.io/libraries/cs50/ !

[@hammadazhar5354]

Can't believe, we have jumped soo many hoops and loops (no pun intended) to reach here finally.

[@ItsSchwifty]

That "pun" was definitely intended

[@nakatopatra2892]

Welcome everyone

[@Sam-px5ff]

2:19:35 Any idea if they found out what happened?

[@NishaStha5104]

Hello there can u put a video of each course in ascending orderly like as if there is pythons part only ...plzz

[@krishnaadhikari7351]

kzbin.info/www/bejne/hIvbcn-sg9F5Y5o Didnt fully understand what you are looking for but this is the full course playlist. you need to enrol at cs50 from edx and this video is a part of it.

[@adityachk2002]

1:02:16 why did he say that… did he mean that people are asking bad questions?

[@sayori3939]

Maybe he's just pointing out on how nobody asks how to make comments since double slashes is used on something else

[@leventebotos6927]

2:03:55 "This will not be in the video"

[@romandzhadan5546]

awesome

[@adrianolesniewicz392]

In terms of the comparison between the speed of the spell checker in C and Python, couldn't you still optimize the hash table or function in the python code to achieve faster, more similar results to C? -- Unless I'm wrong, I'm just assuming this was used as a simple demonstration to highlight why python is typically slower than C...

[@pixelpox11]

He even said that this was a dramatised demonstration:)

[@w0mblemania]

You could do that yes, but extra optimisation requires more work, and there are diminishing returns. And if you're doing more work, you may want to say, simply call a C function or C library in the first place. i.e. mix and match interpreted Python with compiled code. Think of these languages as tools in a toolbox. No one tool does everything perfectly. If you're writing a high performance game engine, you're almost certainly not going to write it in Python. You're going to probably write it in C++. For an Android app, you're probably going to write in Kotlin. If you're writing an iPhone app, you're probably going to write in Swift. However, the *frameworks* (libraries) you use may well be written in C++, for performance reasons. e.g. You may write a web browsing app in Swift for the iPhone, but the underlying Web engine (WKWebView) is actually written in C++.

[@mohamedraffat6814]

really I was hope if i was can study offline with you, you are a fantastic person and very helpful I have liked python from you really

[@caketaster404]

Let me go ahead and say thank you for this

[@caketaster404]

And voila!

[@avinassab2323]

Hey guys , how to access the problem set of the lectures of cs50. Please do reply

[@nnhh6979]

start watching here : cs50.harvard.edu/x/2022/weeks/6/ so much things are there at the bottom of the video like transcripts, codes, problem sets, more explanations and the other lectures are on the left of the screen.

[@ezio510]

Never thought of getting rickrolled while having a lecture lmao

[@BadalKumar-tu2wg]

Great

[@ganbatselenge3042]

lmao different link + no ads

[@armanwirawan7099]

Why are the viewers slowly gets less and less after each lecture? I’m loving this course i watch it everyday

[@duckchen2676]

A lot of people give up while they are teaching themselves how to code. Or if they aren't giving up, they get busy and forget they're doing this or something like that.

[@mrCetus]

The pacing is so fast

[@cavefacts2660]

i like how he says 'whoops'

[@cidhighwind8590]

I watched this lesson twice and I fell for the code at the end twice...

[@Blezerker]

IVE MADE IT THIS FAR! WOOOOOO

[@dunkinDoge]

Well.. my implementation for holmes in C took 29 seconds.... Does this mean i wrote a more advanced languages than python?

[@josephbejarano3755]

The programming language isn't the only thing that plays a part in runtime. Computer hardware and how well your computer can handle tasks is another determining factor of runtime.

[@novacoax]

did I just get Rick Rolled 🤣🤣

[@muhammadessa5406]

where can i found this hogwarts.csv file

[@sayori3939]

Omg why don't most people use this if syntax in PYTHON tutorial (I'm talking about the agree.py)

[@monicagalloriofrio9551]

this is easier.... answer=input("what is your name?") print("hi",answer)

[@landwand]

The day I get Rick-Rolled by Harvard - - -

[@user-hd2fi4gc7t]

Did you pass recover from Problem set 4?

[@someoneyoullmeeteventually6834]

@@user-hd2fi4gc7t I WAS EXHILIRIATED WHEN I FOUND THE SECRET and then I open the link..

[@landwand]

@@user-hd2fi4gc7t Holy! I didn't remember do that PSet and would have let it slide! I'm on Week 6 now; gotta go back and do it.

[@braiinworms]

"all this is coming out of the video" hahah oop

[@Ethernall]

throughout this lecture I kept remembering a song I encountered awhile ago about programming in C. Here's the video for anyone wondering: kzbin.info/www/bejne/qpLWYYJrbZunbpI it's pretty hilarious IMO xD

[@max_unch]

The pandemic version of this crash course with a MASK... Of Course!!! (:/)

[@oliviacolton3661]

Online / edX student here - for the life of me I could not find the source code for blur.py. Where can I find it and how do I download/input it? All the Harry Potter examples come off a little dated (and possibly insensitive) in 2022. I hope he’s using something else this semester.

[@just_a_viewer5]

why do they come off as insensitive?

[@potato-nh5cf]

how dare he rickroll me

[@raicyceprine8953]

13:15 he looks so proud telling the terms operators and operands😂 17:29 that's a real good question. I've already watched a 4 hour python tutorial before watching cs50 and I kinda forgot that that is possible to do in range function. we'll see that answer later on 38:59 i love both their answers but each has different point of view. for me, both is right as well, it really depends on your context but i guess the second answer has a deeper perspective or road to view 42:10 low level language like C is still useful nowadays 1:00:06 ' truncation ' 1:26:11 good thing he pointed this out. i also noticed that before that variables within these while loops are only local to that curly braces but are never really relevant anymore to the whole code. it'll only appear there and only there in the while loop you use it's the second time now that we are discussing about argv and i really still don't get the importance of it at all 2:00:56 if i stumble upon this comment again. i wanna try memorizing this code it looks something useful the 'people[name]' line of code is almost the same as how name->next works so it's kinda familiar 2:02:31 the way he found an alternative solution despite not knowing what was wrong. damn 2:07:35 this is honeslty a good way to use coding, i like it 2:14:15 woah, the code before and after this is cool implementation 2:17:30 no way you could do this in python? so cool

[@TariqYasiinProd]

Yup, just got Rick rolled lol

[@w0mblemania]

Lulz at the ending.

[@getsunova8894]

I got trolled by David.

[@mySDK3333]

🐍

[@liz-uc3yx]

45:19

[@igogo8]

Классный преподаватель,но маска ему не ,,к лицу")

[@redditmmmmmmmmmm3764]

[@docmalc47]

"hello.py"

[@ismailachabi8627]

💙💙

[@rayroman6209]

The pacing is so fast