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What is a while loop?

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Crash Course on Python

4.7（635 個評分） | 24K 名學生已註冊

課程 1（共 6 門，Google IT Automation with Python 專項課程）

This course is designed to teach you the foundations in order to write simple programs in Python using the most common structures. No previous exposure to programming is needed. By the end of this course, you'll understand the benefits of programming in IT roles; be able to write simple programs using Python; figure out how the building blocks of programming fit together; and combine all of this knowledge to solve a complex programming problem. We'll start off by diving into the basics of writing a computer program. Along the way, you’ll get hands-on experience with programming concepts through interactive exercises and real-world examples. You’ll quickly start to see how computers can perform a multitude of tasks — you just have to write code that tells them what to do.

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您將學習的技能

Basic Python Data Structures, Fundamental Programming Concepts, Basic Python Syntax, Python Programming, Object-Oriented Programming (OOP)

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4.7（635 個評分）

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DM

Jan 28, 2020

Very straight forward class. I like the structure of the videos and text to read-along with. The prompts within the video to make sure you're listening was a nice addition.

JM

Feb 07, 2020

Good course for the beginners. It is awesome for beginners. The exercises and the demo in the videos are cool. Balanced course with implementations as well as theory.

從本節課中

Loops

In this module you'll explore the intricacies of loops in Python! You'll learn how to use while loops to continuously execute code, as well as how to identify infinite loop errors and how to fix them. You'll also learn to use for loops to iterate over data, and how to use the range() function with for loops. You'll also explore common errors when using for loops and how to fix them.

Introduction to Loops1:58

What is a while loop?3:12

More while Loop Examples3:14

Why Initializing Variables Matters3:49

Infinite Loops and How to Break Them4:08

教學方

Google

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腳本

[MUSIC] First off, we're going to talk about while loops. While Loops instruct your computer to continuously execute your code based on the value of a condition. This works in a similar way to branching if statements. The difference here is that the body of the block can be executed multiple times instead of just once. Check out this program. Can you guess what it does? Before we execute it to find out, let's go through it together line by line. In the first line we're assigning the value of 0 to the variable x. We call this action initializing, to give an initial value to a variable. In the line after that, we're starting the while loop. We're setting a condition for this loop that x needs to be smaller than 5. Right now we know that x is 0 since we've just initialized it, so this condition is currently true. On the next two lines, we have a block that's indented to the right. Here, we can use what we learned about functions and conditionals to identify that this is the while loop's body. There are two lines in the body of the loop. In the first line, we print a message followed by the current value of x. In the second line, we increment the value of x. We do this by adding 1 to its current value and assigning it back to x. So after the first execution of the body of the loop, x will be 1 instead of 0. Because this is a loop, the computer doesn't just continue executing with the next line in the script. Instead, it loops back around to re-evaluate the condition for the while loop. And because 1 here is still smaller than 5, it executes the body of the loop again. It then prints the message and once more increments x by 1. So the x is now 2. The computer will keep doing this until the condition isn't true anymore. In this example, the condition will be false when x is no longer smaller than 5. Once the condition is false, the loop finishes, and the next line is executed. And finally, the last line of our code prints the last value of x. So now that this code makes a bit more sense, what do you think will happen when we execute it? Ready to find out? Let's execute the code and see what happens. So we had five lines with the message, Not there yet, and then at the end of the script the value of x was 5. This was a simple example of how a while loop behaves. As we've said before, we're learning the building blocks of programming. Once you know those building blocks, you can combine them to create more complex expressions. As an IT specialist, while loops can be super helpful. You can use them to keep asking for a username if the one provided isn't valid, or maybe try an operation until it succeeds. Knowing how to construct these expressions can help you get your computer to do a whole lot with only a little bit of code. It's pretty powerful stuff we're learning here. Now that you've got an idea of how a while loop works, let's spice it up with another example.

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