The Range Function

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University of Michigan 提供のコース

Python Basics

879件の評価

University of Michigan

Python Basics

879件の評価

Specialization Python 3 Programming における 5 の 1 コース

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.

レッスンから

Sequences and Iteration

In week two you will use the lectures and the Runestone textbook to understand the basics of a few python data types - lists, strings, tuples - as well as a control structure - for loops. By the end of this week, you will be able to write more complex programs that create drawings by incorporating for loops. Finally, we will present the basics of an accumulation pattern to you, which will be expanded on in each week for the rest of the course.

The For Loop12:26

The Accumulator Pattern4:58

The Range Function5:05

コースの提供者

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

Welcome back. I previously showed you

the accumulator pattern iterating over a sequence like the numbers from one to 10.

Python actually provides a function for us called the range function.

It takes as an input,

a number and what it produces as an output,

range of five will produce a sequence zero,

one, two, three, four.

So, the sequence it produces has the same number of items as the value that we passed in.

The first element will be zero and then we'll

get all the numbers up to but not including five.

If I say range of 10,

I'll get the integers from zero up to nine.

Now, there's one subtlety to this.

The range function in a real Python implementation doesn't actually produce a list.

It produces what's called an iterable,

something that will generate the numbers zero through

four when we iterate through them in a four loop.

So if I, say for I in range of five it will print out the numbers zero,

one, two, three and four.

If I actually want a real list,

I would have to cast it.

I would take range of five and pass it to

the list function which would turn it into a real list.

Now, in our Runestone environment,

we cheat a little bit and we actually have range of five producing a list object.

So, in the Runestone environment,

you don't strictly speaking have to do this casting of the output to make it a list.

But it's a good idea to get into the habit of doing things like

lines 12 and 13 because in a full Python environment,

if you really wanted to have a list you would have

to take the output of range of five and

pass it to list to cast it into being a real list.

One other thing I want to show you here and then

we'll see the output to check everything we've done.

Range, takes an optional second argument.

So, it actually takes several additional arguments and

we'll have a chance to see what impact this extra argument has.

So, let's run it. Just to match things up here we're just

printing that its range of five and then

lines four and five are producing these numbers zero to four.

That's the same as saying range starting at zero and going up to five.

But if I said range of one five and we'd get something a little different.

Now I would get starting from one up to but not including five.

There's actually an optional third argument that can say

you wanted to increment by a certain amount,

but we won't go into that detail.

Now as I was I was mentioning in the Runestone environment,

range of five comes out as an actual list.

In a full Python interpreter,

it wouldn't be an actual list object unless you first

passed it into the list function to cast it.

The advantage of having the range function,

is that we don't have to write code like on line

one to ask for all the numbers between one and 10.

In fact I'm going to take you back to our code for

the accumulator pattern and show you how it could've been a little simpler.

So, instead of saying,

"nums equals that list",

I could've said, "nums equals range of 1, 11."

I would have gotten the same result of 55.

The range function, will show up as a handy little utility for us throughout

the rest of the specialization and throughout

the rest of your time as a Python programmer.

But keep in mind, the range function can just take

one argument and then

it would give you all the numbers from zero up to but not including 11,

or it can take two arguments where you specify the first item and the last.

So, three to 11 is going to give us less than

55 because we're not including the one and the two.

So, we get 52 instead.

For the range function, takes a number and it gives you

back a sequence like this list of numbers from one to 10.

We'll see you next time.

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