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0:00
Hey everyone, welcome back to this
0:01
channel. Well, this side Raja Lakshmi
0:03
Singum. In today's video, we are going
0:05
to learn something super useful and fun,
0:08
which is how to compare two lists in
0:10
Python. Now, you might be wondering why
0:13
would I even need to compare lists.
0:15
Well, imagine you're making a to-do list
0:18
application and you want to check if the
0:21
tasks the user entered today match the
0:24
tasks they entered yesterday.
0:27
So that's exactly where list comparison
0:30
comes in handy.
0:34
So here's the big idea. We'll take two
0:36
list from the user. Then we'll check if
0:39
they are the same. For two list to be
0:42
the same. So what are the things that we
0:44
have to check is they must have the same
0:47
length and each element should match the
0:50
same order. Sounds simple, right? Let's
0:54
do it step by step.
0:56
So let's start with taking inputs from
1:00
the user
1:07
to list.
1:09
So list one
1:13
input
1:16
just enter the comma separated list.
1:30
and just do dotsplit
1:37
and list to two
1:43
input.
1:47
Enter
1:49
the maybe second
1:53
comma separated list.
2:02
And this will be the first
2:11
comma separated list. And this will be
2:13
the second commaepparated list. And we
2:16
want to split them by
2:19
split method separated with comma. Okay.
2:32
Now let's assume the lists are equal at
2:36
first. So
2:39
let us assume
2:44
the list are equal
2:49
at first.
2:51
So we'll create a variable called equal
2:55
and we'll add true inside that equal
2:58
method.
3:00
So then now it's time to check the
3:03
length of those two lists. So all you
3:06
have to do is first
3:10
check
3:13
if their
3:16
lengths match.
3:20
So if ln of list one
3:27
is equal to ln of list two.
3:34
So when the length of the first three
3:36
len is nothing but the number of items
3:39
that are present in the list like for
3:41
example if the list has three elements
3:43
like 1 2 3 then the number of elements
3:46
in that list is three. So ln will give
3:50
us the quantity of items present in the
3:54
list. So when these two lengths are
3:58
equal. So now
4:01
we will compare elements one by one. So
4:05
now
4:07
compare elements
4:11
one by one
4:14
using a for loop.
4:18
Okay. So how you compare one by one
4:22
especially
4:24
for I in range of len
4:31
of list because how many times you will
4:34
compare obviously the number of times
4:36
the list the number of items are present
4:39
in the list right like for example
4:42
list has 1 2 3
4:46
so the number of times you will count is
4:48
three times which is nothing but the
4:50
maximum count of items present in the
4:53
list which is alen of list one
4:58
right it could be list one or list two
5:01
so if any one of the list is you know
5:05
the size of the list is same then
5:08
obviously if this condition is true that
5:10
means we need just one list length the
5:15
quantity so I'm taking the first one
5:18
itself
5:18
So for in range of ln of list one and
5:23
here you will do it what you will do how
5:26
to access each and every element in the
5:28
list by using the concept of index. So
5:32
if
5:33
list of list one of I don't worry just
5:40
follow the logic we will trace it for
5:42
sure not equal to list
5:46
2 of I
5:50
then if the items are not equal
5:55
obviously the value of equal will be
5:58
false. So equal will now change it to
6:02
false
6:04
and that's it. And now immediately it
6:07
will come out of the loop because we
6:08
don't have to check the other elements.
6:10
Once you see at least one element is not
6:13
matching then you don't have to check
6:14
every element. Once you understood that
6:17
they are not equal you can come out of
6:19
the loop.
6:20
Okay. So this is what the actual logic
6:24
is. And now
6:26
else
6:32
equal
6:34
equal to false.
6:38
Okay. So what's happening here?
6:41
If
6:43
like for example the user gave two
6:45
elements two lists 1 2 and three. Okay.
6:50
If ln of list of one. So what is this
6:52
alien of list of one? The quantity of
6:55
items present in the list. So what is
6:57
the quantity of items present in the
6:59
list? Three. Okay. What is this
7:02
quantity? Three. So if three equal to
7:07
three. Yes, this is true. So now the
7:10
Python program will jump here.
7:13
So now here for i in range of ln of list
7:18
of one. So I obviously if you know about
7:23
the for loop if you know the syntax how
7:25
for loop exactly runs the i actually
7:28
starts with zero okay and the ln of list
7:33
of one is three so is zero in range of
7:37
three true okay so now i value is zero
7:42
so now it's true so now the python jumps
7:45
here if list of i
7:49
See
7:51
list of list one of I what's happening
7:54
here which is nothing but list one of
7:56
zero.
7:59
So list one of 0 is what?
8:05
Listen to me list one of 0 is nothing
8:08
but one. Obviously the concept of index
8:11
is nothing but the position of the
8:14
element in the list. So one is in the
8:18
zeroth position, two is in the first
8:20
position and three is in the second
8:22
position. But the total length of the
8:24
list is three but the positioning the
8:29
indexing starts from zero. So 0 1 2. So
8:34
list one of 0 is 1. Okay. So list one of
8:39
0 is 1.
8:41
And now we want list two of zero.
8:45
So list two of zero
8:50
is
8:52
one itself. So this is list two and you
8:55
want zeroth position which is one. So is
8:58
1 equal to 1 true. But here we are
9:02
checking is 1 not equal to 1. So this
9:06
condition is false. So now the loop goes
9:09
again to the top to the fur loop. Now I
9:13
becomes one
9:16
is one in range of three. Yes.
9:20
If list of one here now the list of zero
9:25
becomes list of one because I value
9:27
changed from 0 to one. So what is the
9:30
list of one value? The first position
9:33
which is nothing but two. Okay. And what
9:37
is the list two of one value? list two
9:40
of one which is nothing but this one. So
9:43
again it will be two. Okay. But two is
9:47
not equal to two is false. So again now
9:52
the Python jumps here and now I value
9:55
becomes two.
9:58
Okay. If list one of two what is list
10:01
one of two? 0 1 2. So this is the list
10:04
one of two which is nothing but three.
10:07
So now it became two and this becomes
10:10
three and list two of two. So list to
10:14
two of two is nothing but this one. So
10:17
it comes here three.
10:20
So three not equal to three. Obviously
10:24
it is false. Then again now the for loop
10:27
the i jumps to three. Is three in range
10:32
of three? No. Right? So now the Python
10:36
program comes out of the loop and it
10:39
will not change the equal false
10:43
and it will come out of the loop. So now
10:45
what is the value of equal?
10:50
I want you to pause. I know you have
10:52
listened to me. I think you have traced
10:54
it with me. Now what is the value of
10:56
equal here? So initially equal value is
10:59
true. So inside this loop it skipped
11:03
this entire if because the condition is
11:06
both are equal. We can see that both are
11:09
equal. So this entire condition is
11:11
skipped. So only for loop
11:14
is running. So if the if condition is
11:18
done so then obviously it will come out
11:22
of the entire loop. So the equal value
11:26
is true itself. So that's the value of
11:29
equal because the list is equal. So
11:32
there is no chance that you can change
11:34
it to false.
11:36
So this is what happened. That's the
11:38
reason I always say I know that you guys
11:40
might fed up saying that use pen and
11:43
paper. But it is really important when
11:44
you are writing each and every line with
11:47
your own mind. Using pen and paper will
11:50
help you definitely uh to think
11:53
logically. Think like computer. Like if
11:56
I write this line, what happens? how
11:58
computer thinks you have to go step by
12:01
step like we did it just now.
12:05
Okay, I will break this down briefly
12:08
once again. So first we asked the user
12:11
to list and we assumed that the list is
12:14
equal. Then we checked the length of
12:17
list. If the lengths are different then
12:20
there is no point of you know going to
12:23
each and every element. So obviously it
12:27
will jump to the else part and it will
12:28
make it false. So if the lengths are the
12:31
same.
12:33
Now we loop through each element
12:36
and we will compare them one by one and
12:39
the moment we find a mismatch we set
12:42
equal to false and we will stop the loop
12:45
by using this break statement. Finally
12:48
we print whether the lists are same or
12:51
not.
12:58
Print the lists are same. Else print the
13:01
lists are different.
13:07
Okay, let's run it.
13:15
1 2 3
13:19
1 2 3
13:22
See if we print the lists are same
13:25
inside the for loop. Every time it is
13:28
running, every time it is printing the
13:30
lists are same. Always always keep that
13:34
in mind. Always try to trace it. So not
13:38
even a single mistake. I did it on
13:40
purpose so that you guys will understand
13:42
the difference.
13:48
Okay, now let's print
13:51
print
13:54
the lists are the same.
14:01
So when they are same if equal
14:08
else
14:10
the lists are
14:14
different.
14:18
So that's it. We have done this kind of
14:22
statement in the previous exercise
14:23
itself. If you guys missed it, I want
14:25
you to go back there, complete that
14:27
exercise and come back here so that you
14:29
will understand because each and in each
14:31
and every exercise I'm explaining you
14:33
something different, something new that
14:36
you guys must get habituated because
14:38
from then on once I explained it I'm
14:41
using it in the next exercise maybe in
14:44
the next programs that we are writing.
14:46
So always please follow each and every
14:49
episode of this tutorial of this entire
14:52
Python beginners course because I would
14:55
suggest you to go through each and every
14:56
minute thing because as a beginner it is
14:58
really important for you to understand.
15:01
The people who are in intermediate stage
15:03
will get the points but the people who
15:05
are really in the beginner stage I want
15:07
you to go through each and everything.
15:10
So that is the reason I'm taking more
15:12
time on each and every episode to you
15:15
know explain it as much as I can.
15:18
So this logic is same as if equal
15:25
just print
15:28
the lists are same
15:35
else
15:37
just print
15:42
the lists are different.
15:48
So this entire logic is same as this
15:51
single line logic. So here we are
15:53
directly doing it inside the print
15:55
itself by using this if condition else.
15:59
So if the condition is true then this
16:01
part will get executed. If condition is
16:04
false then the else part will get
16:06
executed. That's the only difference
16:07
like this is like a bridge. True left
16:11
side, false right side.
16:14
Instead of writing these four lines of
16:16
code, this will optimize the code and
16:18
your code looks more simpler and easier
16:21
to understand. That's the whole point
16:23
is.
16:25
Now let's run this.
16:39
The lists are saying okay.
16:42
What if you want a different list
16:53
the lists are different.
16:56
So finally this is how we will print the
16:58
lists are same or not whether the lists
17:01
are same or not. So this is the entire
17:04
code and see how the comments are you
17:08
know self-explaining the code is
17:10
explained easily explained to even the
17:12
other developer who is looking at our
17:14
code that's the whole point of using the
17:16
comments in every program
17:20
but this is all about the for loop right
17:23
now let's write it in while loop
17:29
okay
17:31
now let's write in while loop.
17:35
So in while loop we will obviously take
17:38
the inputs and we will also keep equal
17:41
equal to true. But the only difference
17:43
is we will initialize the i value to
17:45
zero because in for loop we are using
17:47
the range method. It will initialize it
17:51
by zero itself. But while we have to
17:53
initialize it then it will take from
17:57
then on.
17:59
So I'll just remove this part.
18:03
So here first we'll check if the if the
18:06
len lengths match. So done. And now
18:10
we'll compare the element by element
18:12
using the while loop. So here is the
18:14
entire logic changes.
18:17
So while
18:24
I less than alen of list one. Okay.
18:34
If
18:38
list one of same thing uh there is no
18:41
change. If you observe, if you go
18:43
through the for loop also here we here
18:46
we wrote for I in range of alien of list
18:49
one. But here we are just writing
18:52
while
18:55
I less than
19:00
len of list one.
19:04
That's it.
19:08
while I less than alien of list one. If
19:11
list one of I not equal to list two of
19:16
I, you are writing equal equal to false
19:19
and then you are breaking. But the only
19:21
difference is you have to initialize I
19:24
value zero and also you have to
19:26
increment I value to one for every loop.
19:32
So first round it's zero, next round it
19:34
have to become one, next round it have
19:36
to become two. Don't worry, we'll trace
19:38
it. We'll trace it for sure.
19:43
So that's how you will do it. And then
19:46
you can use else and while also so
19:50
and then you will use this else part. So
19:53
equal equal to false. Okay. Let's run
19:55
this one. Let's trace this one. Okay. If
19:58
ln of list one is nothing but three, we
20:01
are assuming that the value of you know
20:04
the two lists are equal in the beginning
20:06
and we initialize the i value to zero.
20:09
If ln of length list one which is three,
20:13
list two is also three. So 3 equal to 3.
20:17
Is this true? True. Now it jumps here.
20:22
So while i less than what is the value
20:26
of i here? 0 0 less than len of list one
20:31
which is three is 0 less than three true
20:35
so initially I value is zero now if list
20:38
one of zero so what is list one of zero
20:41
the first element not equal to list two
20:44
of zero
20:46
this second list first element is one or
20:49
not equal to one false then again now it
20:53
jumps here now i value becomes
20:57
1 0 + 1 is nothing but one. Is 1 less
21:00
than
21:02
three? True. Now list one of one is
21:08
nothing but the second position two.
21:11
List two of one. The second position is
21:14
two. Is 2 not equal to two? False. So
21:19
again it comes here. It will increments
21:21
the value of i by 1. So this will become
21:25
two.
21:27
Is two less than three? True. So now
21:31
list one of two is nothing but this.
21:35
List two of two is nothing but this one.
21:39
Again is three not equal to three. False
21:43
again. Now I value becomes three. Is
21:46
three less than three? Now listen to me.
21:49
Is three less than three? No. So this
21:53
entire loop will stops. So three less
21:58
than three is false. So it comes out of
22:00
the loop and so it will not even goes to
22:02
this part. So it will just complete this
22:04
part and it will come out of this loop.
22:08
So now what is the value of equal is
22:10
true? Because every time it checks the
22:12
condition it didn't even execute these
22:14
lines. So that means the equal value is
22:17
true. So if equal is true then you will
22:20
print the lists are same. In the same
22:23
way when you give a different value I
22:25
want you to check even for a different
22:28
value so that you will understand why we
22:30
are giving equal equal to false.
22:35
So so
22:39
this one works exactly the same as the
22:41
first code. The only difference is
22:43
instead of for loop we used while
22:48
and here we start from index zero check
22:51
elements one by one and keep moving
22:54
forward until the list ends. If any
22:56
element doesn't match we stop right
22:58
there by using this break. So this is
23:01
how we will complete the logic. So both
23:04
versions solve the same problem just
23:06
using different loops.
23:09
And yeah that's it my friends. I think
23:12
you just learned how to compare two list
23:14
in Python using both fur and while
23:16
loops. If you enjoyed this and found it
23:19
helpful, do me a small favor. Hit the
23:21
like button, share the video with your
23:23
coding buddies, and of course, subscribe
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beginner friendly Python lessons like
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this one. Remember, every big programmer
23:32
once started as a beginner just like
23:35
you. So, keep practicing, keep coding,
23:37
and I'll see you in the next
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