Common Errors

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Из курса от партнера University of Michigan

Python Basics

680 оценок

University of Michigan

Python Basics

680 оценок

Курс 1 из 5 — Specialization Python 3 Programming

This course introduces the basics of Python 3, including conditional execution and iteration as control structures, and strings and lists as data structures. You'll program an on-screen Turtle to draw pretty pictures. You'll also learn to draw reference diagrams as a way to reason about program executions, which will help to build up your debugging skills. The course has no prerequisites. It will cover Chapters 1-9 of the textbook "Fundamentals of Python Programming," which is the accompanying text (optional and free) for this course. The course is for you if you're a newcomer to Python programming, if you need a refresher on Python basics, or if you may have had some exposure to Python programming but want a more in-depth exposition and vocabulary for describing and reasoning about programs. This is the first of five courses in the Python 3 Programming Specialization.

Из урока

General Introduction

In week one you will be introduced to programming in python through lectures and the Runestone textbook - an interactive online textbook built for this course. By the end of the module, you will have run your first python program, and learned how to draw images by writing a program.

Introduction - Debugging1:23

Syntax, Runtime, and Semantic Errors6:40

Know Your Error Messages3:32

Incremental Programming6:29

Common Errors5:38

Conclusion - Debugging1:59

Познакомьтесь с преподавателями

Paul Resnick
Michael D. Cohen Collegiate Professor
School of Information
Steve Oney
Assistant Professor
School of Information
Jaclyn Cohen
Lecturer
School of Information

Let's go through some common errors.

These are typical mistakes that programmers make,

so it would be helpful just to have seen some of

the error messages and how to recognize the problems and how to fix them.

So, one that we've already seen is forgetting a parenthesis.

Here, it tells us there's a syntax error,

it doesn't really know exactly what's wrong but

it tells us there's a syntax error on line six.

Whenever you see a syntax error,

you should always look on the line number that it says.

If everything looks right there,

you should really look on the lines above it.

In this case, we forgot to close the parenthesis on line five.

So, even though it says line six,

it's line six where the Python Interpreter realized there was a problem,

that is on line five where you really have the problem and where you should correct it.

We should add that parenthesis, and now it works.

Our next set of errors involve variable names.

The first thing to realize is that capitalization really matters.

In this case, we go to line three and on line three,

it tries to do capital turtle dot small turtle.

First thing to know is that,

capital turtle and small turtle are

two completely different variable names and small turtle is the name of this module.

In that module, you can find the turtle class.

So, we really need it to have small turtle dot capital turtle.

So, another example of a variable naming problem occurs

here and sometimes you got to watch out and we have a big window to draw in,

that there may be an error message down below.

In this case, the name right is not defined on line six.

You might look at this and say,

this is all just fine,

we're telling june to go right by 90 degrees.

That's not the correct way to say it.

We first have to mention the object and then the dot and then the method.

So, june should go right by 90,

not right dot june.

So, let's fix that.

Now, we get it without the error message.

Here's another variable naming problem.

We create a turtle named June and then we tell June to move right by 90,

again the error messages down

off the screen and it's saying June is not defined on line six.

So, we're telling June to go right,

there's no binding for the variable June.

There is a binding for the variable small j

june but this is a situation where our small j june,

capital J June, not the same variable and so we got that error.

Fix that, no more error there.

Another common type of error is when we invoke

a function but don't pass in the right values,

the right arguments that it's expecting.

So here, we've got a program

where June is supposed to move forward and turn right and do that repeatedly.

But we didn't tell it how many times to do it,

so we invoked the range function but we didn't pass in

an argument saying how many times to do it.

We get an error and it tells us that on line five,

we tried to invoke the range function.

It wanted to have at least one argument but we didn't give it any.

There are no values in the parentheses and it wants at least one.

So, we should have said something like,

do this three times.

Let's give it an argument of three,

and now it works just fine.

So, those are some kinds of common errors that you're

likely to see as you start writing your own programs.

We'll see you next time.

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