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我的钢琴 · App Inventor 2 中文网
...经有什么
打开模板工程，你会看到：
一个 水平布局_琴键行（水平布局），里面已经放了 六个按钮：按钮_E 按钮_F 按钮_G 按钮_A 按钮_B 按钮_高C。
一个 音频播放器_音符（音频播放器组件），非可视组件，排在屏幕下方。
...
Why do we use __init__ in Python classes?
...ical piece of understanding: the difference between a class and an object. __init__ doesn't initialize a class, it initializes an instance of a class or an object. Each dog has colour, but dogs as a class don't. Each dog has four or fewer feet, but the class of dogs doesn't. The class is a concept o...
Hashing a dictionary?
...d make a frozenset with the dict's items and use hash():
hash(frozenset(my_dict.items()))
This is much less computationally intensive than generating the JSON string or representation of the dictionary.
UPDATE: Please see the comments below, why this approach might not produce a stable result.
...
What is the difference between .*? and .* regular expressions?
...edy, first tries to match as many . as possible.
eeeAiiZuuuuAoooZeeee
\_______________/
A.* matched, Z can't match
Since the Z doesn't match, the engine backtracks, and .* must then match one fewer .:
eeeAiiZuuuuAoooZeeee
\______________/
A.* matched, Z still can't match
This ha...
How to get the parents of a Python class?
...
Use the following attribute:
cls.__bases__
From the docs:
The tuple of base classes of a class
object.
Example:
>>> str.__bases__
(<type 'basestring'>,)
Another example:
>>> class A(object):
... pass
...
>>> ...
Header files for x86 SIMD intrinsics
.../x86-64 use x86intrin.h
For gcc/clang/armcc targeting ARM with NEON use arm_neon.h
For gcc/clang/armcc targeting ARM with WMMX use mmintrin.h
For gcc/clang/xlcc targeting PowerPC with VMX (aka Altivec) and/or VSX use altivec.h
For gcc/clang targeting PowerPC with SPE use spe.h
You can handle all t...
Finding the source code for built-in Python functions?
... particular module or function is implemented in you can usually print the __file__ attribute. Alternatively, you may use the inspect module, see the section Retrieving Source Code in the documentation of inspect.
For built-in classes and methods this is not so straightforward since inspect.getfile...
Fastest hash for non-cryptographic uses?
...e all sort of hashes for various purposes. This specific algorithm was the root source of many performance improvements in the current decade.
It's also used in implementations of Bloom Filters. You should be aware that if you're searching for "fast hashes", you're probably facing a typical problem...
What does -> mean in Python function definitions?
...
And the information is available as a .__annotations__ attribute.
– Martijn Pieters♦
Jan 17 '13 at 13:06
9
...
How do I get a PHP class constructor to call its parent's parent's constructor?
.../ main class that everything inherits
class Grandpa
{
public function __construct()
{
}
}
class Papa extends Grandpa
{
public function __construct($bypass = false)
{
// only perform actions inside if not bypassing
if (!$bypass) {
}
// call Gra...