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理解Python字典上的max函数操作(Understanding the max function operation on Python dictionary)

 我试图理解Python字典上max函数的操作。 以下是我使用的代码：  
tall_buildings = { 
    "Empire State": 381, "Sears Tower": 442,
    "Burj Khalifa": 828, "Taipei 101": 509 
}


# 1. find the height of the tallest building
print("Height of the tallest building: ", max(tall_buildings.values()))


# 2. find the name, height pair that is tallest
print(max(tall_buildings.items(), key=lambda b: b[1]))


# 3. find the tallest building
print(max(tall_buildings, key=tall_buildings.get))
 
 所有上述打印语句都给出了正确的结果，如代码中的注释所示。  
 我理解#1和#2是如何工作的。  
 
  1： tall_buildings.values()给出一个高度流， max函数返回高度的最大值。  
  2： tall_buildings.items()给出（名称，高度）对的流，并且max函数根据key=pair's height.返回该对key=pair's height.  
 
 但是，我很难理解# 3是如何工作的。 key=tall_buildings.get如何成为寻找最高建筑的关键？  
 我从Ned的Pycon Talk中获取了代码： https ：//youtu.be/EnSu9hHGq5o ？ t = 12m42s 

I am trying to understand the operation on max function on Python dictionary. Following is the code I am using: 
tall_buildings = { 
    "Empire State": 381, "Sears Tower": 442,
    "Burj Khalifa": 828, "Taipei 101": 509 
}


# 1. find the height of the tallest building
print("Height of the tallest building: ", max(tall_buildings.values()))


# 2. find the name, height pair that is tallest
print(max(tall_buildings.items(), key=lambda b: b[1]))


# 3. find the tallest building
print(max(tall_buildings, key=tall_buildings.get))
 
All the above print statements gives the correct results as indicated in the comments in the code.  
I understood how #1 and #2 works. 
 
 1: tall_buildings.values() gives a stream of heights and max function returns the max of the heights. 
 2: tall_buildings.items() gives a stream of (name, height) pairs and max function returns the pair based on the key=pair's height. 
 
However, I have difficulty in understanding how # 3 works. How does key=tall_buildings.get serve as the key for finding the tallest building ? 
I have taken the code from Ned's Pycon Talk: https://youtu.be/EnSu9hHGq5o?t=12m42s

原文：https://stackoverflow.com/questions/44566537

更新时间：2022-05-21 12:05

最满意答案

 为什么不在你要停止的帧处使用javascript的setTimeout函数？  
...
  if (iteration < totalIterations) {
      iteration++;
  } else {
      iteration = 0;
      moveRight = !moveRight;
  }

  if (iteration == 0 && moveRight){
    setTimeout(function(){ 
      requestAnimationFrame(drawCircle); 
    }, 3000);
  }else{
    requestAnimationFrame(drawCircle);
  }
...
 
 码本的例子  
 如果你害怕setTimeout函数的不准确，另一个选项是：  
  if (iteration < totalIterations) {
      iteration++;
  } else {
      iteration = 0;
      moveRight = !moveRight;
  }

  if (iteration == 0 && moveRight){
    var next_iter = new Date().getTime() + 3000;
    delay_restart(next_iter);
  }else{
    requestAnimationFrame(drawCircle);
  }

}
drawCircle();

function delay_restart(start) {
  while (new Date().getTime() < start ){

  }
  requestAnimationFrame(drawCircle)
}
 
 codepen的第二个例子 

Why not use javascript's setTimeout function at the frame you want to stop? 
...
  if (iteration < totalIterations) {
      iteration++;
  } else {
      iteration = 0;
      moveRight = !moveRight;
  }

  if (iteration == 0 && moveRight){
    setTimeout(function(){ 
      requestAnimationFrame(drawCircle); 
    }, 3000);
  }else{
    requestAnimationFrame(drawCircle);
  }
...
 
codpen example 
another option in case you're scared of the inaccuracy of the setTimeout function: 
  if (iteration < totalIterations) {
      iteration++;
  } else {
      iteration = 0;
      moveRight = !moveRight;
  }

  if (iteration == 0 && moveRight){
    var next_iter = new Date().getTime() + 3000;
    delay_restart(next_iter);
  }else{
    requestAnimationFrame(drawCircle);
  }

}
drawCircle();

function delay_restart(start) {
  while (new Date().getTime() < start ){

  }
  requestAnimationFrame(drawCircle)
}
 
codepen for second example

理解Python字典上的max函数操作(Understanding the max function operation on Python dictionary)

最满意答案

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