Understanding Selection Solution - Intro to Computer Science Udacity English Japanese

Understanding Selection Solution - Intro to Computer ScienceYouTube↗ IA↗(long shot)
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So here's the answer. The first one is always equivalent to

解答です　1つ目は文字列sと常に同じです

the string s, remember what it means to use the colon when there's nothing on the left side means, start from the beginning, and

コロンの左辺が空白の場合は最初から開始し

when there's nothing on the right side, means go all the way

右辺が空白だと終わりまで選択します

to the end. So if there's nothing on on either side, that's

両側に何もない場合は

selecting the entire string. So the second one's a little trickier, but

全部の文字列を選択します 2つ目は少し分かりにくいです

this also always has the same value as the string s. And

これも文字列sと常に同じ値になります

the reason is, we have the original string s, and we're concatenating to it the string s index 0, colon negative

その理由は元の文字列sがありそれに［0：－1＋1］を連結するからです

1 plus 1. Well, negative 1 plus 1 has the

－1＋1はゼロになりますね

value 0. When we index from 0 colon 0, that's an empty string. And the reason that's an empty string

［0：］の場合は空の文字列になります

is because we're starting from 0. And we're stopping just

ゼロから開始しゼロの前で終了するからです

before 0, there are no character between 0 and 0

ゼロとゼロの間に文字はなく

so that's an empty string. Adding the empty string to

文字列は空です　空の文字列を

itself, leaves the string empty. And the interesting thing about

空の文字列に追加すると空の文字列が残ります

this is, this works even when s is an

sが空の文字列でも機能するのです

empty string. If s was an empty string, s index

もしsが空の文字列だったらs［0］になります

0. That would produce an error. It's trying to

これはエラーになります

select the first character from s, and there is no

sから1つ目の文字を選択しようとしても空なので

first character since s was an empty string. But

1つ目の文字がありません

s index 12 colon 12, even though there is no 12th character of, of s, since there is no

［12：12］ならsが12文字なくても

characters between there, it's okay that s doesn't have them.

間に文字がないので大丈夫です

That's going to valuate to the empty string. So, the third

空の文字列を評価することになります

one is also always equivalent to s. It's selecting from the

3つ目もsと常に等しくなります文字列の始めのゼロの位置から

beginning of the string, position 0, all the way to

終わりまで全部選択します

the end. Again, as we saw here, even if s has

ここで見たのと同じで

no characters, this is still okay. It will give us

sに文字がなくても大丈夫です空の文字列が与えられます

the empty string, if s has any characters, it will give us all the characters in s. This first one is not

sに文字があるとsの全部の文字が与えられます 4つ目は等しくありません

equivalent, and this might be a little surprising. It sounds like,

これには少し驚くかもしれません

well, it's selecting all the characters from the beginning to the end, because negative 1 is the index of

－1はsの最後の文字のインデックスなので全部の文字を選択します

the last character in s. But remember that the selection stops before the last character. So what this do, will

最後の文字の前で選択が終了することを覚えておいてください

do will give us every character besides the last one.

この場合最後の文字を除くすべての文字が与えられます

So let's see that in the Python interpreter. Were going

Pythonインタプリタで確認しましょう

to print s index, colon, negative one, and this will

print s［：－1］です　これを実行します

give us all the characters except for the last one.

最後を除く全部の文字が表示されます

So the final one is the most surprising. That this actually

最も驚くのは最後の選択肢が

is always equivalent to s. It's equivalent even if s has fewer

常にsと等しくなります　sが3文字未満の場合でもです

than 3 characters. So the first part of selecting all the characters from the beginning up to position three, not including position three,

最初の部分で始めから3の位置までの文字を全部選びます　3の位置の文字は含みません

and then we're concatenating that with all the characters of s from position 3 to the end. If s has less than 3

それにsの3の位置から最後までの文字を連結します

characters, well this is going to be empty. There are no characters

もしsが3文字未満なら空になります

from position 3 to the end. But that's okay, we're going to

3から終わりまで文字がありませんが大丈夫です

add the empty string to the characters before position 3. So here's how that works in

3の位置の前の文字に空の文字列を加えます

the python interpreter. We'll do s from position

これがPythonインタプリタのやり方です sの最初の位置から

beginning to index 3 and add that s to index 3 to the end. That produces the same string. And if we do this with a

index3までを行いそのsをindex3から終わりまでに加えます同じ文字列が作られます短い文字列でこれを行う場合

shorter string. Let's initialize t to be the string, Hi. We can print from

tを文字列Hiと設定してみましょう tから3の位置までと

t to position 3 plus from t to position 3 to the end. We don't get an error.

tの3の位置から終わりまでを表示しますエラーは出ません

We get the string Hi out. So, this indexing

文字列Hiが現れますインデックス化した部分列は柔軟で

subsequences is very resilient. It works even when we index positions that don't exist in the string. This is

文字列に存在しない位置をインデックス化しても機能します

different from when we were doing indexing of particular positions

これはある特定の位置のインデックス化とは異なります

by themselves. If we did index t, index 3,

もしt［3］としたらエラーが出ます

that will give us an error. Because there's no character at position 3.

なぜなら3の位置に文字がないからです

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