大约有 48,000 项符合查询结果（耗时：0.0631秒） [XML]
How do I perform the SQL Join equivalent in MongoDB?
...rect. The new $lookup operator added to the aggregation pipeline is essentially identical to a left outer join:
https://docs.mongodb.org/master/reference/operator/aggregation/lookup/#pipe._S_lookup
From the docs:
{
$lookup:
{
from: <collection to join>,
localField: <...
What is the advantage of GCC's __builtin_expect in if else statements?
...
I guess it should be something like:
cmp $x, 0
jne _foo
_bar:
call bar
...
jmp after_if
_foo:
call foo
...
after_if:
You can see that the instructions are arranged in such an order that the bar case precedes the foo case (as opposed to the C code). This can utilise the CPU ...
Fastest way to list all primes below N
...4.0 |
| sundaram3 | 416.0 |
+---------------------+-------+
Of all the methods tested, allowing numpy, for n=1000000,
primesfrom2to was the fastest tested.
+---------------------+-------+
| Method | ms |
+---------------------+-------+
| primesfrom2to | 15.9 |
| p...
Can I use __init__.py to define global variables?
I want to define a constant that should be available in all of the submodules of a package. I've thought that the best place would be in in the __init__.py file of the root package. But I don't know how to do this. Suppose I have a few subpackages and each with several modules. How can I access th...
Is there a list of screen resolutions for all Android based phones and tablets? [closed]
...p the extreme aspect ratios, that are rarely seen at phone size or larger, all the other devices fit a range from 1.3333 to 1.7778, which conveniently matches the current iPhone/iPad ratios (considering all devices in portrait mode). Note that there are quite a few variations within that range, so i...
In Python, how do I determine if an object is iterable?
...e a method like isiterable ? The only solution I have found so far is to call
21 Answers
...
Can't pickle when using multiprocessing Pool.map()
...nsider it "easy" or not;-) is to add the infrastructure to your program to allow such methods to be pickled, registering it with the copy_reg standard library method.
For example, Steven Bethard's contribution to this thread (towards the end of the thread) shows one perfectly workable approach to a...
How can I create a copy of an object in Python?
...would like to create a copy of an object. I want the new object to possess all properties of the old object (values of the fields). But I want to have independent objects. So, if I change values of the fields of the new object, the old object should not be affected by that.
...
node.js global variables?
...
Globals are generally to be avoided, but if you really want to use them. The 3 statements below are all equivalent and will assign a var to the global scope: GLOBAL._ = require('underscore'); global._ = require('underscore'); _ = require('und...
How can I time a code segment for testing performance with Pythons timeit?
...r if you want to average the time elapsed by several runs, you have to manually call the function multiple times (As I think you already do in you example code and timeit does automatically when you set its number argument)
import time
def myfast():
code
n = 10000
t0 = time.time()
for i in ran...