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App Inventor 2 连接方式：AI伴侣、模拟器、USB · App Inventor 2 中文网
...局域网内吗？
A：旧的兼容模式的测试原理是电脑端启动Web服务供手机连接，两者必须在同一局域网内。
但是最新版升级了通信方式（Webrtc技术）后去除了这一限制，经验证手机、电脑任意的网络环境下均可正常测试，欢迎体...
Python None comparison: should I use “is” or ==?
...ject None, so when you do my_var is None, you're checking whether they actually are the same object (not just equivalent objects)
In other words, == is a check for equivalence (which is defined from object to object) whereas is checks for object identity:
lst = [1,2,3]
lst == lst[:] # This is Tr...
How to check file input size with jQuery?
...
You actually don't have access to filesystem (for example reading and writing local files), however, due to HTML5 File Api specification, there are some file properties that you do have access to, and the file size is one of them.
F...
Find the files existing in one directory but not in the other [closed]
...rison is to use find with md5sum, then a diff.
Example:
Use find to list all the files in the directory then calculate the md5 hash for each file and pipe it to a file:
find /dir1/ -type f -exec md5sum {} \; > dir1.txt
Do the same procedure to the another directory:
find /dir2/ -type f -exe...
Loop through all nested dictionary values?
I'm trying to loop through a dictionary and print out all key value pairs where the value is not a nested dictionary. If the value is a dictionary I want to go into it and print out its key value pairs...etc. Any help?
...
Valid content-type for XML, HTML and XHTML documents
...st for registered media types ending in +xml.
(For unregistered x- types, all bets are off, but you'd hope +xml would be respected.)
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MongoDB Many-to-Many Association
... user document:
{name:"Joe"
,roles:["Admin","User","Engineer"]
}
To get all the Engineers, use:
db.things.find( { roles : "Engineer" } );
If you want to maintain the roles in separate documents then you can include the document's _id in the roles array instead of the name:
{name:"Joe"
,roles:...
Avoid browser popup blockers
...m javascript that is not invoked by direct user action. That is, you can call window.open in response to a button click without getting hit by the popup blocker, but if you put the same code in a timer event it will be blocked. Depth of call chain is also a factor - some older browsers only look a...
Utility classes are evil? [closed]
...d object-oriented design, most classes should represent a single thing and all of its attributes and operations. If you are operating on a thing, that method should probably be a member of that thing.
However, there are times when you can use utility classes to group a number of methods together ...
Why is TypedReference behind the scenes? It's so fast and safe… almost magical!
...ecification, the constructs used to implement them under the hood (vararg calling convention, TypedReference type, arglist, refanytype, mkanyref, and refanyval instructions) are perfectly documented in the CLI Specification (ECMA-335) in the Vararg library.
Being defined in the Vararg Library makes ...