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Hey friends, welcome back to another
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Python beginner series video. Well, this
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Sai Raja Lakmi Singum and today's
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program looks super simple, but I
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promise you it's going to teach you a
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very powerful concept. We are going to
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take a list of numbers and if the first
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number is negative, we'll replace it
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with zero. But here is the cool part.
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I'll first show you how to do it
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manually and then we'll understand the
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importance of something called map in
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Python. And yes, we'll solve this with
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both for loop and while loop so you get
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So step one is to take the numbers from
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the user and if the first number is
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negative replace it with zero and step
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three you will print the modified list.
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Sounds easy right? But the way we write
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it matters a lot. Let's first do it
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without map. Okay. First let's take the
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and you'll do dotsplit.
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And if I enter -5 10 20 as the input. So
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that gives me -5 10 20 in string format.
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Let's check by just printing my list
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10 20. So these are not numbers. These
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are actually strings. So we need to
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convert each element to numbers. So what
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I do for that we use for loop. Okay.
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len of my list. Guys we have done it
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multiple times. I think now you know why
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are we using this range method and why
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we need the alien to get the actual size
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of the list. And in that according to
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that we are going to change and my list
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let's run it and check again. But before
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that let's print my list.
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See now it changed to numbers. Okay. Now
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what we have to do? We have to check
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whether the first element in the list is
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negative or not. If it's negative then
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we have to replace it with zero. Okay.
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So again for that we are going to do for
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So if the first element i =0 and
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then you will make it
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then you will just come out of the loop
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okay so what's happening here for i in
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range of ln of my list
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okay what is ln of my list for exam
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Example here you gave
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- y 10 20 as input. Okay. So because of
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this it converted to integers. Let's say
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let's assume that these are numbers not
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the strings. So for i in range of ln of
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my list. What is this ln of my list? The
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number of items present in the list. So
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the number of items present in the list
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is three. So ln of my list is three. So
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I in range of three. That means I starts
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from zero and runs until I becomes
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So initially what is the value of i?
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So if I =0 and my list of i less than
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zero that means the first position is
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you're checking whether is that a first
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position and at the same time that first
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position is less than zero or not. So i
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equal to0 and my list of zero is nothing
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but we are accessing the first element
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in the list. So which is this one and we
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are checking whether it is less than
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zero because we have to check whether
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the number is negative or not. So how
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you check whether a number is negative
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or not when it is less than zero
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obviously we will say that number is a
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negative. So my list of i less than
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zero. So if these two conditions are
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true then only this statement will get
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executed. So then the first element will
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and then you will immediately come out
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of the loop because you don't have to do
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any other modifications in the list. You
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don't have to change any other elements.
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You just need the first element and you
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just have to access it and you check
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whether it is less than zero or not and
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then you will print according to the
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result by doing it to zero. So this is
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So you will just print that
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is something like this. And when you run
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the modified list is 0 10 20. So this is
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But notice how we had to manually
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convert each and every element. This
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thing that's a bit long, right?
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So here is where Python makes life
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easier. Instead of converting one by
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one, we can just say my list of
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And we need this for list. So just keep
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So list of map of int comma input. You
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don't have to write this logic.
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You can do it just like this. You're
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saying that hey python take every item
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in the list and turn it into an integer
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for me. And it does that in one line.
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One single line. You don't have to write
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for loop. You don't have to like you
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don't have to write multiple lines of
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code. Now it looks so clean, short and
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professional hooking code,
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See no change at all. So that is the
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importance of map. The reason I didn't
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say is because first you guys must
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understand the syntax of map. So that is
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why in previous video I didn't explain
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but this is all the actual importance of
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map. So it will actually convert each
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and every element in the list to
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integer. So that is why we use map.
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Okay. Now it's time to work with the
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while loop. As usual, we'll take the
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numbers and we'll use map here. And then
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next, we check the first element in a
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loop. Always remember in while loop, you
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have to initialize it to zero. So I'm
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initializing it to zero. And you will do
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I less than len of my list everything is
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same. Then you will come out of the
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loop. Here I'm not incrementing I by one
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because I just need the first value. So
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it will just come out of the loop. So
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this is what happening. So let's run it.
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That's it. Everything is same. Same
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result just a different way of looping
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through the list. This helps you
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understand how both for and while loops
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can solve the same problem. And here is
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something super important to remember is
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in our earlier exercises I didn't use
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map. Why? Because I wanted you to first
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understand the basics of lists and
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loops. And now that you are comfortable
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and I wanted you to see the beauty of
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map so it makes our code more shorter
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and cleaner and even easier to read. So
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there you go my friends. We learned how
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to replace the first element of list if
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it's negative using both for and while
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loops. Also remember programming is like
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learning to ride a bicycle. At first you
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take the longer path step by step and
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then one day you just learn the
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shortcuts that make the ride smoother.
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If this video made coding feel simple
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and clear, do me a tiny favor. Hit that
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subscribe button because here we are not
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just writing Python programs. We are
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building your confidence one small step
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Keep practicing, keep coding, and I'll
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see you in the next lesson.
