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MQTT客户端内置版使用指导 · App Inventor 2 中文网
...入口。
案例一：连接并订阅
when 按钮_连接.Click() {
MqttClient1.Connect(true)
}
when MqttClient1.ConnectionStateChanged(新状态, 状态文本) {
标签1.Text = 状态文本
if MqttClient1.IsConnected {
MqttClient1.Subscribe("demo/status", 0)
}
}
...
Abstract methods in Python [duplicate]
...mething along these lines, using ABC
import abc
class Shape(object):
__metaclass__ = abc.ABCMeta
@abc.abstractmethod
def method_to_implement(self, input):
"""Method documentation"""
return
Also read this good tutorial: http://www.doughellmann.com/PyMOTW/abc/
You can...
How to merge lists into a list of tuples?
...
In Python 2:
>>> list_a = [1, 2, 3, 4]
>>> list_b = [5, 6, 7, 8]
>>> zip(list_a, list_b)
[(1, 5), (2, 6), (3, 7), (4, 8)]
In Python 3:
>>> list_a = [1, 2, 3, 4]
>>> list_b = [5, 6, 7, 8]
>>> list(zi...
Determine the type of an object?
...
On instances of object you also have the:
__class__
attribute. Here is a sample taken from Python 3.3 console
>>> str = "str"
>>> str.__class__
<class 'str'>
>>> i = 2
>>> i.__class__
<class 'int'>
>>> class...
Regex lookahead, lookbehind and atomic groups
...pression.info for more details.
Positive lookahead:
Syntax:
(?=REGEX_1)REGEX_2
Match only if REGEX_1 matches; after matching REGEX_1, the match is discarded and searching for REGEX_2 starts at the same position.
example:
(?=[a-z0-9]{4}$)[a-z]{1,2}[0-9]{2,3}
REGEX_1 is [a-z0-9]{4}$ which...
One-liner to check whether an iterator yields at least one element?
...In case the iterator yields something false-ish you can write any(True for _ in iterator).
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Calling constructors in c++ without new
...d the most common way of creating new dynamic objects instead of using auto_ptr, unique_ptr, or related.
– Fred Nurk
Jan 18 '11 at 13:18
3
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Getter and Setter?
...
You can use php magic methods __get and __set.
<?php
class MyClass {
private $firstField;
private $secondField;
public function __get($property) {
if (property_exists($this, $property)) {
return $this->$property;
}
}
publi...
Should I use 'has_key()' or 'in' on Python dicts?
...
in is definitely more pythonic.
In fact has_key() was removed in Python 3.x.
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How to make rpm auto install dependencies
...
No, this will not work unless libtest1-1.0-1.x86_64.rpm is in a repository elsewhere, or both packages are specified on the command line like "rpm -i" would require. I just verified this on yum 3.4.3 (Fedora 18). Transcript here showing that it goes to the updates repo for...