Variables and types
Python for IGCSE CS Lesson 2 2:21 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Ask for someone's age and you get back the text seven, not the number seven.
你问别人的年龄，拿回来的是文字的七，不是数字的七。
That difference is about to cost you an answer.
这个差别，马上就会让你算错一道题。
A variable is a named box that holds a value.
变量是一个装着值的、有名字的盒子。
You put a value in with an equals sign, and that act has a name in the syllabus: assignment.
你用等号把值放进去，而这个动作在考纲里有个名字：赋值。
Worth noticing before the exam — the exam draws an arrow pointing left instead of an equals sign.
考试前值得注意一点—— 考卷上画的是一个向左的箭头，而不是等号。
Same action, different symbol, and the arrow is arguably clearer: it shows the value moving into the name.
同一个动作，不同的符号， 而且箭头可以说更清楚：它显示了值正在进入那个名字。
The syllabus names exactly five data types, and you can be asked to list them.
考纲刚好列出五种数据类型，而且可能会让你把它们写出来。
Integer is a whole number and real is a decimal.
integer 是整数，real 是小数。
Char is a single letter and string is text of any length.
char 是单个字符，string 是任意长度的文本。
And Boolean holds only true or false.
而 Boolean 只装 true 或 false。
Python calls three of those something else — int, float, str — so when the exam asks, answer with the exam's names.
其中三种在 Python 里叫别的名字——int、float、str—— 所以考试问的时候，要用考纲的说法来回答。
A constant is a value that never changes while the program runs — pi, a tax rate, the number of days in a week.
常量是程序运行期间永远不变的值—— 圆周率、税率、一周的天数。
The exam has a keyword for it.
考卷上有专门的关键字。
Python does not, so the convention is to write it in capitals.
Python 没有，所以约定是把它的名字写成大写。
Be honest about what that means: nothing stops you changing it.
这里要说实话：并没有什么能阻止你去改它。
The capitals are a message to whoever reads the code next, including you in a month.
大写是写给下一个读这段代码的人看的， 包括一个月后的你自己。
Because input hands you text, you will convert constantly, and there are three to know.
因为 input 交给你的是文本，你会不停地做转换，有三个要记住。
Int makes a whole number.
int 得到整数。
Float for a decimal.
float 得到小数。
And str turns a number back into text, which you need when you join it onto a message.
而 str 把数字变回文本，当你要把它拼进一句话时就需要它。
Now the three tasks: an area, a total cost, and a number read in and increased by three.
现在做那三道题： 一个面积，一个总价，还有一个读进来再加 3 的数字。
Four things to take with you.
带走四点。
One: a variable is a named box, filled by assignment.
第一：变量是一个有名字的盒子，通过赋值来填充。
Two: the five types are integer, real, char, string and Boolean.
第二：五种类型是 integer、real、char、string 和 Boolean。
Three: a constant never changes — write its name in capitals.
第三：常量永远不变——它的名字写成大写。
Four: int, float and str convert between types.
第四：int、float 和 str 用来做类型转换。
Now do the three tasks.
现在去做那三道题。