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Debugging Python for Beginners (with most common Examples)
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Feb 24, 2025
In this tutorial, we will learn about the most common things that can go wrong with your code. We will also learn how to read and debug Python errors (traceback). ## Top 10 Most Common Exceptions in Python 1. SyntaxError 2. IndentationError 3. ValueError 4. ModuleNotFoundError 5. IndexError 6. AttributeError 7. TypeError 8. NameError 9. FileNotFoundError 10. KeyError ----- Install Python: - MacOS: https://www.jcchouinard.com/install-python-on-macos/ - Windows: https://www.jcchouinard.com/install-python-on-windows/ - Anaconda: https://www.jcchouinard.com/install-python-with-anaconda-on-windows/
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0:00
hi everyone my name is Ja in this
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beginner Python tutorial I'm going to
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show you one of this most useful skills
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you can have in your python tool sets
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when you start
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programming and that is debugging your
0:14
code inevitably you will end up with
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some code errors at some point and you
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want to be able to look at this and know
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what to do so the first step I'm going
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to show you is I created a code with
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that create an error and I'm going to
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show you what happens here I'm ending up
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with what we call the trace back and you
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want to be able to read that Trace back
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and be able to debug it because you're
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going to see that a lot of time so when
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you read this I made you a small uh
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visualization that can help you is you
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start reading from the bottom to the top
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and the first thing that you look at is
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the name the exception of the exceptions
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names that you're seeing and right there
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I'm getting the name error and I have
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some information that says name is not
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defined this gives me a hint that I
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haven't defined a variable somewhere and
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I want to look further and I start from
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the file with the actual error so I can
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see that code with error.
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pi has this function which is make hello
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which I called there in my code
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so the higher you are in your Trace back
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the closer you are to what you executed
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so you first executed this make Alo and
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then in order to execute this you call a
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function that is found in your code with
1:52
error right there and I could
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potentially go back to my code with
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error and I can see that the name
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variable was not defined so that's how
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you try to debug uh your Trace
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back uh you also have the the the line
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number where it happens uh and a lot of
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useful
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information now you want to learn the
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main exception types what kind of
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exceptions will you encounter in your
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life what kind of Errors uh and they
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fall back back into three main
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categories and those main categories are
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uh the uh syntax errors the exceptions
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and The Logical
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errors why they have these categories is
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because they're not going to behave the
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same way if you have a syntax error
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nothing will work uh code will break and
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the code block will not be running at
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all it will just throw the error
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instantly and how you get that Sy syntax
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error is if I do well true for example
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and I say
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print
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one in that case it would print one
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forever but since I forgot my uh column
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here then I throw a syntax error and
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nothing else can can can work you have
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the exceptions and you have the logical
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errors the exception is a bit different
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is that it won't break because of a
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syntax error but when you try to do it
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during runtime it will break so if you
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try to do a zero division error for
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example zero division so 9 divided by 0o
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inevitably you will get a zero division
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error but the code could run because if
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I come back here to my w true and I say
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print I uh like I want to print I right
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above here uh you can see that it didn't
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print the letter i before running but if
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I put it above my runtime execution then
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I can see that it printed the I first
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but then return the zero division error
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and that's what we mean by runtime
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error as for logical error uh it will
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not show any uh ER like exceptions like
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the syntax or the except the the runtime
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errors but it will had your code won't
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behave as what you would have expected
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so one common example is if I have a
4:34
equal 5 and b equal 10 and what I want
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to do is I want to sum a plus b and then
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multiply by two uh one thing that you
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might happen is a logical error so I can
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I will print that logical error so let's
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say I want to do 5 + 10 * 2 I do a + b *
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2 if I run this I end up with a problem
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because 5 + 10 * 2 is supposed to be 30
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and in this case it's 25 and the reason
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because that is because it
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did 5 + 10 * 2 so it did did 25 so if I
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want to fix that logical error what I
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need to do is simply put in parentheses
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like you would do in math and then you
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have your fixed
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errors now that we went into the main
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categories of Errors there are multiple
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exceptions that you will encounter in
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your life if you want to show all the
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types of exception you can do print
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there
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locals and then let's
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say thunder net
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built-ins
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thunder so what you'll get here you will
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have a list of all the possible syntax
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errors uh but I'm going to cover the top
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10 most exception uh most common
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exceptions that you will encounter the
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first thing and we already mentioned
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this is the syntax error and the syntax
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error will happen with if it will happen
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uh if blocks try and except blocks while
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blocks and uh for I in range blocks and
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the way this often happens is if you
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forgot to put your column right there
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and you Tred to do so
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if uh a equals B and then you try to
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print a equals
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B then you try this and that's what we
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just saw it it happens all the time uh
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whenever you forgot a column this is one
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of the thing that you'll see the most
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often
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this happens also when you have a
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string and you want to forget
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to you forget to put the uh closing
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string element
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unclosed so if I try to do this I will
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have an exception uh syntax error that
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says you haven't terminated your string
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literal deted a line to and as you can
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see that error I was always start with
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the name and then I see some information
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and I didn't even go up because I knew
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it was because it wasn't closed it's
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easy at over time you get a sense of
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those errors and you spot them
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instantly another
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big potential errors that you will
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encounter is the indentation error the
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indentation error happens when you
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haven't intented your block and this is
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very important because uh um python
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forces you to have some syntax to follow
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up and and if you don't it will break so
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it forces you to have that s that that
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um that indentation and in this case
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otherwise you get indentation error in
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order to fix this you just add a tab and
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then press and it
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works um otherwise you have other
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situation when you define a function
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and you have something that is
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print properly
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indented and when you don't follow
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always the same indentation right now vs
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code just tells me that it's okay it
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just puts it automatically there but
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let's I try to do it manually or I paste
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code from somewhere else and like
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somebody made that error and you have
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uneven and then this will throw an
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indentation error and as you can see I
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didn't even have to try to call the
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function for this to break because it is
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part of the syntax error python wants
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you to have a proper syntax it makes you
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a better programmer because it makes
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your code beautiful but it does throw
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some of these
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exceptions let's say I see the third
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biggest uh culprit is a value error so
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if you try to convert for example a
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string to a int like that works right
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you can change an in uh a number one to
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a number one in integer but if you try
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to do this by changing a string then you
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will have an exception that breaks
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because you're actually trying to change
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text to an integer which doesn't work uh
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it can also happen if you do a float and
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then you have a string that is three 0
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22 like if you have this how do you
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convert this to a float you cannot
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convert it because there's two dot
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notation another very common use case is
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if you have a package and that happens
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all the time you get code you import it
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from a tutorial that you found online
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and then they ask you to import request
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HTML and then you try to run it and you
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have module not found
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error
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um the only way to fix this the simple
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way to fix this is to just do a pip
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install so generally you have the PIP
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install and you have your uh
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requests HTML for example and you just
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run this and in your uh terminal and you
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would fix your
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error there are other kind of imports
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that can break so if you try to import
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Panda for example but you call it pandu
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you're going to have the same error if
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you do import Panda and that's very
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important because you want your casing
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to be always pandas like normal with the
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like the proper import would be Panda so
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you have to fix your casing and it will
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not tell you what the error is but you
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can spotted by the wrong casing here
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you will get index error as well so here
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I have three values so I can take my
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list and index zero and I will get the
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first item of my list but what if I take
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an item that is larger than the list has
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then I can see list index out of range
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that happens very very very
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often another exception that you will
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face is when you are trying to uh make
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make a reference of something that does
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not exist so if you try to append the
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the number four to the list uh then you
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will have my list will work but if you
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try to do add
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five let let's run this it works so if I
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if I return my
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list it works fine
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what if I try to add A5 to the to the
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letter it doesn't work because add is
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not uh a method that you can uh use on a
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list item and you will get the attribute
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error next let's get into the type
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errors and type errors can happen very
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very often and in this case what how
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we're going to fix this is you take your
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result and you when you try to match a a
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to an integer for example you have a
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mismatch type and that will break one
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thing that you can do is you could say
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convert this to a string instead and you
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would fix your type error there are
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other issues when you try to index uh
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something that is not indexable so you
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take this and you try to get the index
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Zero from an integer you cannot do this
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but you would be able to do it on a
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string for example uh so that's one of
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the cases
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if you try to call a non-callable object
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so remember when you want to do a uh
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caller function you just use this
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notation but if you try to do this on a
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list you will get the type error list
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object is not
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callable also if you have a variable
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that is equal none and then you try to
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append something or make a calculation
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on it plus equal 5 then you will get
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this Ty typ error to uh you have other
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situation when you have incompatible
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types comparison I won't go into too
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much detail uh they're all uh variable
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that happens one that happens very often
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is when you try to assign a value and
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you're get the unable type list this is
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come up very often and when you have a
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type mismatch integer equal 3.4
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14 uh earlier we talked about the name
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error and that's very simple if I try to
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call my variable I never created that
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variable vs code is very smart it just
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tells me what it's in white I can see it
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easily that it does not even exist so if
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I run it I automatically get the name
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error and that's when you never defined
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it so if you say my variable equals 5
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and then you call my variable as you can
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see the variable became blue and it
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doesn't break
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anymore next we have IO error this
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happens a little less but it generally
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happens when you try to open a file that
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does not exist
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nonexistent file. text and I just try to
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do as F and I do content or even just F
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read so if I try to read that file I get
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the file not found error which is
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essentially an IO error um you depending
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on your version you might see both uh
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the next uh error that you will see is
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the key
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error
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um and this occurs when you have a
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dictionary and you try to access a key
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that doesn't exist so let's take that uh
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dictionary and I want to select the
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letter A the the key
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a I will be able to return the letter
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one but let's say if I try to access a
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key that does not uh get then I can see
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key error and it doesn't
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exist if you want to prevent those
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runtime errors that we discussed uh like
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this you're trying to print one divided
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by zero you can use try and accept so
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you use
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try and
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accept
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print the what and
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error so as you can see here we used to
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have a zero division error but now it
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works properly didn't throw an error
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didn't break anything if I want to do
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any something else uh it will still
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work
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something it will still print it but it
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Returns the the error if you want to go
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further and have a better knowledge of
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what's going on then you can do
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exception as e and then you rate it so
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what will happen is that will store the
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exception name into your uh EV variable
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and then you can return show it the
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error and then you see it uh the uh try
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and except return that was an error and
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gave you where what the error was uh
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which is super useful in your code to
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handle all the potential exceptions and
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um that's it so we covered almost
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everything we need to know for the most
17:52
common use cases where you encounter
17:55
error feel free to subscribe to my
17:57
channel H or or visit my blog on jar.com
18:02
and uh feel free to like And subscribe
18:05
bye
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