This article selects the world's second largest same-sex dating website StackOverflow Most praised in the world 10 A question , The total number of likes exceeded 5 ten thousand , Considering a lot of white whores , There are at least 10 Ten thousand people are interested in these problems ！
So many people like it , Explain two questions ：
1. These questions are very common , When programming, we often encounter
2. These questions are not simple , Otherwise you don't have to go to the forum
this 10 A question , Some are complicated , Some are simple . How many do you know ？ Leave a comment in the comments section .
I was going to explain 10 A question , But because of the space , This article covers only one of the most frequently asked questions , Subsequent articles may cover a number of issues .
Now let's focus on the first question ：
The problem is all Python Top of the list of problems ：
Yield What is the key word ？
Consider the following code ：
def _get_child_candidates(self, distance, min_dist, max_dist):
if self._leftchild and distance - max_dist < self._median:
yield self._leftchild
if self._rightchild and distance + max_dist >= self._median:
yield self._rightchild
This is the calling code ：
result, candidates = [], [self]
while candidates:
node = candidates.pop()
distance = node._get_dist(obj)
if distance <= max_dist and distance >= min_dist:
result.extend(node._values)
candidates.extend(node._get_child_candidates(distance, min_dist, max_dist))
return result
When _get_child_candidates When called , What happened? ？ Returned a list Do you ？ It's still an element ？ Will it be tuned over and over again ？ When do subsequent calls stop ？
Looking a little confused ？ You can continue to look at the solution , And then come back to the question .
To understand yield, To understand first generators, To understand generators To understand first iterable( Iterable ).
Iterables
When you create 1 individual list, You can read it one by one , It's called iteration ：
>>> mylist = [1, 2, 3]
>>> for i in mylist:
... print(i)
1
2
3
above mylist It's a iterable( Can be iterated ). When you use a list derivation , You create a list , That's one iterable:
>>> mylist = [x*x for x in range(3)]
>>> for i in mylist:
... print(i)
0
1
4
So you can use for…in… What syntax traverses is iterable：list, str, file wait
these iterable It is useful to , You can cycle through them . But all of their values are in memory . If your list There is 10 100 million strings , To create this list It's going to be slow , And it takes up a lot of memory , So we need Genertor.
Generators
Generator yes iterable, Can be recycled . But it's not the same as above , It can only be cycled once . It doesn't keep all the values in memory , They dynamically generate the values of the elements in the loop .
>>> mygenerator = (x*x for x in range(3))
>>> for i in mygenerator:
... print(i)
0
1
4
This generator is almost the same as the list derivation , The only difference is the use of parentheses (), Not brackets []. but , You can't use it twice for i in mygenerator, Because the generator can only be cycled once ： They calculate 0x0, Return results , I don't keep it myself , Next time you call it , He calculated 1x1, And so on .
Yield
Yields It's a key word , It can be understood as and return equally , The difference is that it returns a generator.
>>> def createGenerator():
... mylist = range(3)
... for i in mylist:
... yield i*i
...
>>> mygenerator = createGenerator() # create a generator
>>> print(mygenerator) # mygenerator is an object!
<generator object createGenerator at 0xb7555c34>
>>> for i in mygenerator:
... print(i)
0
1
4
The above example creates range, Has taken up memory , But the square doesn't take up . This example is not very good , This is the original author's example , There should be a better example in my video .
First , because yield The existence of , When you call the function above , The code is not executed , Instead of returning a Generator.
And then there's the key ：
Now let's look at the first question ：
This is a tree traversal algorithm , Find the eligible nodes in the tree . Detailed Chinese comments are added to the code .
Generator:
# This function returns a generator (Generator), This is a binary tree node Methods in objects
def _get_child_candidates(self, distance, min_dist, max_dist):
# If there's a left child , And the distance meets the requirements , Back to the left child , And then pause here
if self._leftchild and distance - max_dist < self._median:
yield self._leftchild
# If there's a right child , And the distance meets the requirements , Back to right child , And then pause here
if self._rightchild and distance + max_dist >= self._median:
yield self._rightchild
# If it's done here , It means that there are no qualified left and right children , The generator is empty , It's the end of the iteration .
Caller:
# Create an empty list , And the current object node
result, candidates = list(), [self]
# loop , In the beginning, it was just myself
while candidates:
# Pop up the last node
node = candidates.pop()
# get obj The distance between the object and the target node
distance = node._get_dist(obj)
# If distance ok, Write to the result list
if distance <= max_dist and distance >= min_dist:
result.extend(node._values)
# Add your own child node to the candidates in , So the cycle will continue , Until all the nodes in the tree are traversed
candidates.extend(node._get_child_candidates(distance, min_dist, max_dist))
return result
Learn from good examples Python Whether it's employment or sideline, it's good to make money , But learn to Python Still have a learning plan . Finally, let's share a complete set of Python Learning materials , For those who want to learn Python Let's have a little help ！
Python All directions are Python Sort out the common technical points , Form a summary of knowledge points in various fields , The use of it is , You can find the corresponding learning resources according to the above knowledge points , Make sure you learn more comprehensively .
If a worker wants to do a good job, he must sharpen his tools first . Study Python Common development software is here , It saves you a lot of time .
When we were watching videos to learn , You can't just move your eyes and brain without hands , A more scientific way to learn is to use them after understanding , At this time, the hand training program is very suitable .
Optical theory is useless , Learn to knock together , Do it , Can you apply what you have learned to practice , At this time, we can make some practical cases to learn .
We learn Python Must be to find a well paid job , The following interview questions are from Ali 、 tencent 、 The latest interview materials of big Internet companies such as byte , And the leader Ali gave an authoritative answer , After brushing this set of interview materials, I believe everyone can find a satisfactory job .
Guarantee 100% free 】
Who says straight men cant confess? Valentines day teaches you to send love in Python code
Its today 214 Valentines Day ,
Python Tkinter - Chapter 9 method of multi selection button control (checkbutton)
9.2 How to select multiple but
