ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: #62 Python Tutorial for Beginners | Generators
กำลังสร้างบทเรียน...
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Welcome back aliens, my name is Davin Reddy and in this video we'll talk about generators.
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Now in the earlier video we have talked about iterators.
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So normally we use iterators to print or to fetch one value at a time.
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So let's say if you have a list of values, let's say 100 values, And if you want one by one value, what makes sense is to use iterator.
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But there are small issues with iterator right?
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The first one you need to get the iterator where you have to define those two functions.
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Next and iter.
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We don't want to do that.
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We want Python to do it for us.
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And that's where Python says, okay, if you want iterators, we will give you generators.
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Okay, but now you will think we have two different concepts.
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Not exactly.
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Generators will give you iterators.
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Our job is done, right?
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So generator give you iterator.
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But how exactly to create a generator?
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So let's do that.
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So what I will do is I will just jump to Another file which is gen .py, you can create your own file there.
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And here let me define a function.
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That's right, we have to define a function, not a class this time.
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So let's say our function define and we'll do the same thing, we'll return the top 10 values.
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So we'll say top 10 and this will return the top 10 value and I will call this as well.
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So I will let me just say I have values and this will be top 10.
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So top 10 is.
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a function which will give you the iterator.
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But hold on, a function cannot give you the iterator, right?
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A function has to be something special.
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So we have to convert this function into a generator.
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And the way to do that is, Normally in function we write return, right?
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So if you say return 5, so this values will be having 5.
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But if you instead of saying return 5, if you say
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e -gildify your job is done because e -gildify your special keyword which will make your function as a generator.
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but now you will think what's the difference even return will
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give you the value even it will also give you the
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value what i will do is i will just go back here let me just print the value
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and if you run this code
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so you can see we got a different thing instead of
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getting a value 5 we got a object of generator
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and that's the thing you know because generator gives you an iterator
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so this function is not a normal function this is a generator because we are using yield yes if you will be different.
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A will also return the value back it will return in the format of a iterator.
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And everyone knows if you want to fetch something from an iterator, we have to use the next Let's run this code and you can see we got 5.
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But now you will think, okay, that's fine.
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Even return give the same output, right?
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No, there's a difference.
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In yield, since it's a generator which will give you iterator, you can write multiple yield statements.
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So let's say yield 1.
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Let's copy this.
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Let's do it for four times and then they will be having different values here 2, 3 and 4.
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Now you can see we got 4 yield which is 1, 2, 3, 4 and if you run this code, you will only get the first value because you are saying next only once.
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So this is same as iterator where you are getting multiple values, right?
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So you got your own iterator without using next and iterator function.
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Let me just do that one more time.
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I will say next.
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Yes, you can also say next and in bracket you can say valves.
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That's a choice you have.
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Otherwise, this will work.
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You can see we got one, two.
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In fact, we can also use a loop.
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So let's use a loop.
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I will say for I in valves.
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I'll let you print I here.
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The moment you do that, you can see it will print all the values for you.
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The remaining values which is three and four.
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This is how you can create the rate up just by using that one particular keyword which is yield.
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Okay, now there is another example we can take here.
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Example, let's say I want to print top 10 perfect square.
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You can do that.
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So let's create one.
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So what I will do is I will just remove this part.
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Okay, because the logic will change.
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Everything else will remain same.
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Let me just not do this.
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Let's use a for loop to print all the values.
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But what should be logic?
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So what I will do is I will say I will take a variable
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which is i initially or maybe n will do n is equal to 1
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and now since we want to print all the perfect square we have to use a loop.
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I will not be using a for loop here because indirectly for uses iterator.
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Let's use while so I will say while n less than equal to 10
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because we want to fetch top 10
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and every time you find a new value you have to just have to say yield.
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You can say sq is equal to n into n that's how you find a square.
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Once you got this square you can simply say yield and you can say sq.
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Okay, so we are sending the value right.
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So it is almost same as return but then return will terminate the function this will not.
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That's something you have to remember.
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Now, once you say sq you have to say n
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because you have to also iterate your n right you have
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to say n plus is equal to one i guess our job is done this should work let's try
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so i will just run this application
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and you can see we got top 10 perfect square we got 1 4 9 16 25
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so that's how you can do it
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because this yield will give you the next next value
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because see when you say you're running a loop you're fetching one by one value
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so when you fetch the first value this yield will return one when the loop says hey i value, it will give you nine.
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So that's how you create a iterator using a generator.
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But the question is why someone will use a generator?
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Think about this.
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Let's say you are fetching 1000 records from a database.
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So when you say you're fetching 1000 records, maybe you want to print all, or maybe you want to process something from those records.
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So when you say you want to fetch 1000 records, all these 1000 records will be loaded in your memory.
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We don't want that.
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Maybe you want to work with one value at a time.
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So let's say 1000 records, we want to work with one value at a time.
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In that case, you can use generator instead of using, instead of fetching the entire list, you can fetch one by one value.
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So that's something you can do with generator.
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That's maybe you can call as a real -life example.
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So this is how we use generator with the help of yield keyword.
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So I hope you enjoyed this video.
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Let me know in the comment section and do subscribe for other videos.
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Bye.
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you
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Vocabulary and speaking notes for this lesson
This B1 speaking lesson is built on the video “Python Tutorial for Beginners”. The speaker keeps coming back to these words: value, iterator, generator, function, return. This video has 113 sentences and 1240 words to shadow. The speech runs for 6:02. The speaker talks fast, about 206 words per minute, so expect linked and reduced sounds. 86% of the words are among the 3,000 most common in English; the rest is worth studying before you start.
Key vocabulary in this video
The 15 most advanced words in the video, with pronunciation and meaning:
| Word | Pronunciation | Meaning |
|---|---|---|
| iterator noun | One who or that which iterates. | |
| generator noun | /ˈdʒɛnəɹeɪtə(ɹ)/ | An apparatus in which vapour or gas is formed from a liquid or solid by means of heat or chemical process, as a steam boiler, gas retort etc. |
| yield verb | /jiːld/ | To give as a result or outcome; to produce or render. |
| fetch verb | /fɛt͡ʃ/ | To retrieve; to bear towards; to go and get. |
| loop noun | /luːp/ | A length of thread, line or rope that is doubled over to make an opening. |
| define verb | /dɪˈfaɪn/ | To determine with precision; to mark out with distinctness; to ascertain or exhibit clearly. |
| keyword noun | /ˈkiː.wɜːd/ | Any word used as the key to a code. |
| valve noun | /ˈvælv/ | A device that controls the flow of a gas or fluid through a space, such as a pipe, manifold, or plenum. |
| iterate verb | /ˈɪtəɹeɪt/ | To perform or repeat an action on each item in a set. |
| terminate verb | /ˈtɝmɪneɪ̯t/ | To end something, especially when left in an incomplete state. |
| indirectly adverb | /ˌɪn.dɪˈɹɛk(t).li/ | In an indirect manner. |
| bracket noun | /ˈbɹækɪt/ | A fixture attached to a wall to hold up a shelf. |
| subscribe verb | /səbˈskɹaɪb/ | To write (one’s name) at the bottom of a document; to sign (one's name). |
| convert verb | /kənˈvɝt/ | To transform or change (something) into another form, substance, state, or product. |
| variable adjective | [ˈvæɹ.i.ə.bl̩] | Able to vary or be varied. |
Phrasal verbs you will hear
| Word | Meaning |
|---|---|
| go back verb | To return to a place or state after having been there at a previous time. |
Sentences worth repeating
Short, complete lines from the video that you can reuse in everyday conversation:
- We don't want to do that.
- That's a choice you have.
- I'll let you print I here.
- That's something you have to remember.
ไวยากรณ์ในวิดีโอนี้
โครงสร้างที่ผู้พูดใช้บ่อยที่สุด พร้อมคำพูดจริงจากวิดีโอ:
| โครงสร้าง | ในวิดีโอ |
|---|---|
| ประโยคเงื่อนไข if + อนุประโยค, will/would + กริยา — เงื่อนไขและผลลัพธ์ | if you want iterators, we will give · if you run this code, you will only |
| Relative clauses who / which + อนุประโยค — ข้อมูลเพิ่มเติมเกี่ยวกับคนหรือสิ่งของ | file which is · function which will · keyword which will |
| Passive voice be + กริยาช่อง 3 — เน้นสิ่งที่เกิดขึ้น ไม่ใช่ผู้กระทำ | is done · will be loaded |
| คำแนะนำด้วย “should” should + กริยา — บอกสิ่งที่ควรทำ | should be · should work |
Pronunciation to watch
The speaker uses 10 contractions and reduced forms, such as we'll, you're, don't. Say them the short way, as you hear them.
- Long words — get the stress right: generator /ˈdʒɛnəɹeɪtə(ɹ)/, indirectly /ˌɪn.dɪˈɹɛk(t).li/
How to practise with this video
- Listen to the whole video once without speaking and note the words you do not know.
- Start at 0.75× speed, shadow it sentence by sentence, then go back to normal speed once it feels easy.
- Record yourself and compare with the original, paying attention to words like iterator, generator, yield.
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