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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
-----
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0:00
hi everyone my name is Ja in this
0:02
beginner Python tutorial I'm going to
0:04
show you one of this most useful skills
0:07
you can have in your python tool sets
0:09
when you start
0:10
programming and that is debugging your
0:14
code inevitably you will end up with
0:17
some code errors at some point and you
0:20
want to be able to look at this and know
0:22
what to do so the first step I'm going
0:25
to show you is I created a code with
0:29
that create an error and I'm going to
0:31
show you what happens here I'm ending up
0:34
with what we call the trace back and you
0:38
want to be able to read that Trace back
0:40
and be able to debug it because you're
0:43
going to see that a lot of time so when
0:46
you read this I made you a small uh
0:49
visualization that can help you is you
0:52
start reading from the bottom to the top
0:56
and the first thing that you look at is
0:59
the name the exception of the exceptions
1:02
names that you're seeing and right there
1:04
I'm getting the name error and I have
1:07
some information that says name is not
1:10
defined this gives me a hint that I
1:13
haven't defined a variable somewhere and
1:17
I want to look further and I start from
1:21
the file with the actual error so I can
1:24
see that code with error.
1:27
pi has this function which is make hello
1:31
which I called there in my code
1:35
so the higher you are in your Trace back
1:38
the closer you are to what you executed
1:41
so you first executed this make Alo and
1:46
then in order to execute this you call a
1:50
function that is found in your code with
1:52
error right there and I could
1:55
potentially go back to my code with
1:56
error and I can see that the name
1:59
variable was not defined so that's how
2:02
you try to debug uh your Trace
2:07
back uh you also have the the the line
2:11
number where it happens uh and a lot of
2:15
useful
2:19
information now you want to learn the
2:21
main exception types what kind of
2:24
exceptions will you encounter in your
2:26
life what kind of Errors uh and they
2:29
fall back back into three main
2:32
categories and those main categories are
2:36
uh the uh syntax errors the exceptions
2:40
and The Logical
2:42
errors why they have these categories is
2:45
because they're not going to behave the
2:47
same way if you have a syntax error
2:50
nothing will work uh code will break and
2:53
the code block will not be running at
2:55
all it will just throw the error
2:57
instantly and how you get that Sy syntax
3:00
error is if I do well true for example
3:04
and I say
3:06
print
3:07
one in that case it would print one
3:10
forever but since I forgot my uh column
3:13
here then I throw a syntax error and
3:16
nothing else can can can work you have
3:20
the exceptions and you have the logical
3:23
errors the exception is a bit different
3:26
is that it won't break because of a
3:28
syntax error but when you try to do it
3:31
during runtime it will break so if you
3:33
try to do a zero division error for
3:36
example zero division so 9 divided by 0o
3:40
inevitably you will get a zero division
3:43
error but the code could run because if
3:46
I come back here to my w true and I say
3:49
print I uh like I want to print I right
3:54
above here uh you can see that it didn't
3:59
print the letter i before running but if
4:02
I put it above my runtime execution then
4:05
I can see that it printed the I first
4:08
but then return the zero division error
4:11
and that's what we mean by runtime
4:14
error as for logical error uh it will
4:17
not show any uh ER like exceptions like
4:21
the syntax or the except the the runtime
4:24
errors but it will had your code won't
4:28
behave as what you would have expected
4:30
so one common example is if I have a
4:34
equal 5 and b equal 10 and what I want
4:38
to do is I want to sum a plus b and then
4:41
multiply by two uh one thing that you
4:45
might happen is a logical error so I can
4:48
I will print that logical error so let's
4:51
say I want to do 5 + 10 * 2 I do a + b *
4:58
2 if I run this I end up with a problem
5:02
because 5 + 10 * 2 is supposed to be 30
5:07
and in this case it's 25 and the reason
5:09
because that is because it
5:11
did 5 + 10 * 2 so it did did 25 so if I
5:16
want to fix that logical error what I
5:19
need to do is simply put in parentheses
5:23
like you would do in math and then you
5:25
have your fixed
5:27
errors now that we went into the main
5:30
categories of Errors there are multiple
5:33
exceptions that you will encounter in
5:35
your life if you want to show all the
5:37
types of exception you can do print
5:40
there
5:44
locals and then let's
5:47
say thunder net
5:51
built-ins
5:53
thunder so what you'll get here you will
5:57
have a list of all the possible syntax
6:02
errors uh but I'm going to cover the top
6:05
10 most exception uh most common
6:08
exceptions that you will encounter the
6:11
first thing and we already mentioned
6:13
this is the syntax error and the syntax
6:16
error will happen with if it will happen
6:19
uh if blocks try and except blocks while
6:22
blocks and uh for I in range blocks and
6:28
the way this often happens is if you
6:31
forgot to put your column right there
6:35
and you Tred to do so
6:37
if uh a equals B and then you try to
6:43
print a equals
6:47
B then you try this and that's what we
6:50
just saw it it happens all the time uh
6:54
whenever you forgot a column this is one
6:56
of the thing that you'll see the most
6:58
often
7:00
this happens also when you have a
7:02
string and you want to forget
7:05
to you forget to put the uh closing
7:09
string element
7:12
unclosed so if I try to do this I will
7:16
have an exception uh syntax error that
7:18
says you haven't terminated your string
7:22
literal deted a line to and as you can
7:25
see that error I was always start with
7:29
the name and then I see some information
7:31
and I didn't even go up because I knew
7:34
it was because it wasn't closed it's
7:36
easy at over time you get a sense of
7:39
those errors and you spot them
7:44
instantly another
7:46
big potential errors that you will
7:49
encounter is the indentation error the
7:52
indentation error happens when you
7:54
haven't intented your block and this is
7:57
very important because uh um python
8:01
forces you to have some syntax to follow
8:05
up and and if you don't it will break so
8:09
it forces you to have that s that that
8:13
um that indentation and in this case
8:16
otherwise you get indentation error in
8:18
order to fix this you just add a tab and
8:20
then press and it
8:22
works um otherwise you have other
8:25
situation when you define a function
8:32
and you have something that is
8:35
print properly
8:40
indented and when you don't follow
8:43
always the same indentation right now vs
8:45
code just tells me that it's okay it
8:48
just puts it automatically there but
8:50
let's I try to do it manually or I paste
8:53
code from somewhere else and like
8:55
somebody made that error and you have
8:58
uneven and then this will throw an
9:02
indentation error and as you can see I
9:05
didn't even have to try to call the
9:07
function for this to break because it is
9:09
part of the syntax error python wants
9:13
you to have a proper syntax it makes you
9:16
a better programmer because it makes
9:18
your code beautiful but it does throw
9:21
some of these
9:23
exceptions let's say I see the third
9:26
biggest uh culprit is a value error so
9:30
if you try to convert for example a
9:33
string to a int like that works right
9:36
you can change an in uh a number one to
9:40
a number one in integer but if you try
9:43
to do this by changing a string then you
9:46
will have an exception that breaks
9:48
because you're actually trying to change
9:50
text to an integer which doesn't work uh
9:54
it can also happen if you do a float and
9:57
then you have a string that is three 0
10:01
22 like if you have this how do you
10:04
convert this to a float you cannot
10:06
convert it because there's two dot
10:11
notation another very common use case is
10:15
if you have a package and that happens
10:19
all the time you get code you import it
10:21
from a tutorial that you found online
10:24
and then they ask you to import request
10:26
HTML and then you try to run it and you
10:30
have module not found
10:32
error
10:33
um the only way to fix this the simple
10:37
way to fix this is to just do a pip
10:40
install so generally you have the PIP
10:42
install and you have your uh
10:45
requests HTML for example and you just
10:49
run this and in your uh terminal and you
10:53
would fix your
10:56
error there are other kind of imports
10:59
that can break so if you try to import
11:01
Panda for example but you call it pandu
11:04
you're going to have the same error if
11:06
you do import Panda and that's very
11:09
important because you want your casing
11:11
to be always pandas like normal with the
11:14
like the proper import would be Panda so
11:17
you have to fix your casing and it will
11:20
not tell you what the error is but you
11:22
can spotted by the wrong casing here
11:30
you will get index error as well so here
11:33
I have three values so I can take my
11:36
list and index zero and I will get the
11:38
first item of my list but what if I take
11:41
an item that is larger than the list has
11:45
then I can see list index out of range
11:48
that happens very very very
11:52
often another exception that you will
11:55
face is when you are trying to uh make
11:59
make a reference of something that does
12:00
not exist so if you try to append the
12:04
the number four to the list uh then you
12:08
will have my list will work but if you
12:14
try to do add
12:19
five let let's run this it works so if I
12:24
if I return my
12:26
list it works fine
12:30
what if I try to add A5 to the to the
12:33
letter it doesn't work because add is
12:36
not uh a method that you can uh use on a
12:40
list item and you will get the attribute
12:45
error next let's get into the type
12:47
errors and type errors can happen very
12:51
very often and in this case what how
12:53
we're going to fix this is you take your
12:55
result and you when you try to match a a
12:59
to an integer for example you have a
13:01
mismatch type and that will break one
13:03
thing that you can do is you could say
13:06
convert this to a string instead and you
13:09
would fix your type error there are
13:12
other issues when you try to index uh
13:15
something that is not indexable so you
13:18
take this and you try to get the index
13:20
Zero from an integer you cannot do this
13:23
but you would be able to do it on a
13:25
string for example uh so that's one of
13:28
the cases
13:30
if you try to call a non-callable object
13:33
so remember when you want to do a uh
13:36
caller function you just use this
13:39
notation but if you try to do this on a
13:41
list you will get the type error list
13:43
object is not
13:45
callable also if you have a variable
13:48
that is equal none and then you try to
13:52
append something or make a calculation
13:54
on it plus equal 5 then you will get
13:58
this Ty typ error to uh you have other
14:02
situation when you have incompatible
14:05
types comparison I won't go into too
14:08
much detail uh they're all uh variable
14:12
that happens one that happens very often
14:15
is when you try to assign a value and
14:18
you're get the unable type list this is
14:22
come up very often and when you have a
14:25
type mismatch integer equal 3.4
14:32
14 uh earlier we talked about the name
14:35
error and that's very simple if I try to
14:38
call my variable I never created that
14:41
variable vs code is very smart it just
14:44
tells me what it's in white I can see it
14:47
easily that it does not even exist so if
14:50
I run it I automatically get the name
14:53
error and that's when you never defined
14:55
it so if you say my variable equals 5
14:58
and then you call my variable as you can
15:01
see the variable became blue and it
15:04
doesn't break
15:08
anymore next we have IO error this
15:12
happens a little less but it generally
15:15
happens when you try to open a file that
15:18
does not exist
15:22
nonexistent file. text and I just try to
15:27
do as F and I do content or even just F
15:33
read so if I try to read that file I get
15:37
the file not found error which is
15:39
essentially an IO error um you depending
15:44
on your version you might see both uh
15:47
the next uh error that you will see is
15:51
the key
15:53
error
15:54
um and this occurs when you have a
16:00
dictionary and you try to access a key
16:03
that doesn't exist so let's take that uh
16:05
dictionary and I want to select the
16:09
letter A the the key
16:12
a I will be able to return the letter
16:15
one but let's say if I try to access a
16:18
key that does not uh get then I can see
16:21
key error and it doesn't
16:26
exist if you want to prevent those
16:28
runtime errors that we discussed uh like
16:32
this you're trying to print one divided
16:34
by zero you can use try and accept so
16:37
you use
16:39
try and
16:43
accept
16:47
print the what and
16:51
error so as you can see here we used to
16:54
have a zero division error but now it
16:57
works properly didn't throw an error
17:00
didn't break anything if I want to do
17:02
any something else uh it will still
17:06
work
17:07
something it will still print it but it
17:10
Returns the the error if you want to go
17:13
further and have a better knowledge of
17:17
what's going on then you can do
17:20
exception as e and then you rate it so
17:24
what will happen is that will store the
17:26
exception name into your uh EV variable
17:29
and then you can return show it the
17:32
error and then you see it uh the uh try
17:35
and except return that was an error and
17:38
gave you where what the error was uh
17:42
which is super useful in your code to
17:44
handle all the potential exceptions and
17:47
um that's it so we covered almost
17:50
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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