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How can I get nth element from a list?
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Look here, the operator used is !!.
I.e. [1,2,3]!!1 gives you 2, since lists are 0-indexed.
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App Inventor 2 手机蓝牙及语音控制 - App Inventor 2 中文网 - 清泛IT论坛，有思想、有深度
...标】
1.掌握蓝牙客户端或服务端组件的使用；
2.学会编写手机蓝牙APP，并向Arduino发送控制指令；
3.学会编写手机语音控制程序，并能通过语音控制Arduino等设备。 【项目范例】
1. 情境
通过对APPInvent...
How to parse float with two decimal places in javascript?
... toFixed() to do that
var twoPlacedFloat = parseFloat(yourString).toFixed(2)
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How do I compute derivative using Numpy?
...d choice.
Here is an example using SymPy
In [1]: from sympy import *
In [2]: import numpy as np
In [3]: x = Symbol('x')
In [4]: y = x**2 + 1
In [5]: yprime = y.diff(x)
In [6]: yprime
Out[6]: 2⋅x
In [7]: f = lambdify(x, yprime, 'numpy')
In [8]: f(np.ones(5))
Out[8]: [ 2. 2. 2. 2. 2.]
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What is /dev/null 2>&1?
...v/null has the same net effect. I usually just use > for that reason.)
2>&1 redirects standard error (2) to standard output (1), which then discards it as well since standard output has already been redirected.
sh...
App Inventor 2 中文网 · 项目指南
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How to avoid overflow in expr. A * B - C * D
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120
This seems too trivial I guess.
But A*B is the one that could overflow.
You could do the follo...
Can I get JSON to load into an OrderedDict?
...ecoder(object_pairs_hook=collections.OrderedDict).decode('{"foo":1, "bar": 2}')
OrderedDict([('foo', 1), ('bar', 2)])
>>>
You can pass this parameter to json.loads (if you don't need a Decoder instance for other purposes) like so:
>>> import json
>>> from collections i...
How to update Python?
I have version 2.7 installed from early 2012. I can't find any consensus on whether I should completely uninstall and wipe this version before putting on the latest version.
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~x + ~y == ~(x + y) is always false?
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237
Assume for the sake of contradiction that there exists some x and some y (mod 2n) such that
~...