$xdg-mime default firefox.desktop x-scheme-handler/http #默认用firefox打开http链接

$pip3 install you-get # pip 安装
$you-get -i URL # 查看视频信息，如标题，分辨率，大小等
$you-get -F {hd2,mp4} URL # 选择某一个分辨率下载

alias python='rlwrap python'
alias maxima='rlwrap maxima'
alias guile='rlwrap guile'

$youtube-dl -F URL # 列出所有可供下载的格式，每个前面有一个ID
$youtube-dl -f ID  # 下载指定格式的码流
$youtube-dl -f bestaudio URL # 下载质量最好的音频码流，下载音乐和有声读物时很有用，之前不知道，还专门找从youtube上下mp3的网站，当时就怀疑，这些网站不可能是自己下载视频后再提取音频的，不然太慢了！

>>> arr = [[0] * 3] * 3
 [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> arr[0][0] = 1
>>> print arr
 [[1, 0, 0], [1, 0, 0], [1, 0, 0]]

>>> [id(x) for x in arr]
 [140692558271840, 140692558271840, 140692558271840]

>>> a = [0] * 3
>>> print a
 [0, 0, 0]
>>> a[1] = 1
>>> print a
 [0, 1, 0]

>>> [id(x) for x in arr]
 [23646576, 23646576, 23646576]

>>> arr = [[ 0 for i in xrange(3)] for j in xrange(3)]
>>> arr = [[ 0] * 3 for i in xrange(3) ]

mpl.matplotlib_fname() #显示matplotlibrc文件的位置。

# The default backend; one of GTK GTKAgg GTKCairo GTK3Agg GTK3Cairo
# CocoaAgg MacOSX Qt4Agg Qt5Agg TkAgg WX WXAgg Agg Cairo GDK PS PDF SVG
# Template.
# You can also deploy your own backend outside of matplotlib by
# referring to the module name (which must be in the PYTHONPATH) as
# 'module://my_backend'.
backend      : GTKAgg
# If you are using the Qt4Agg backend, you can choose here
# to use the PyQt4 bindings or the newer PySide bindings to
# the underlying Qt4 toolkit.
#backend.qt4 : PyQt4        # PyQt4 | PySide
# Note that this can be overridden by the environment variable
# QT_API used by Enthought Tool Suite (ETS); valid values are
# "pyqt" and "pyside".  The "pyqt" setting has the side effect of
# forcing the use of Version 2 API for QString and QVariant.

ln -s /etc/fonts/conf.avail/70-no-bitmaps.conf /etc/fonts/conf.d

$ ln -s /etc/fonts/conf.avail/09-texlive-fonts.conf /etc/fonts/conf.d/09-texlive-fonts.conf

int a[10] = {[5] = 4, [8] = 13};
int b[10] = {[2 ... 5] = 4, [8 ... 9] = 13};

$ fortune -c | cowthink -f $(find /usr/share/cows -type f | shuf -n 1)
 _______________________________________
( (songs-poems) % Volcanoes have a      )
( grandeur that is grim And earthquakes )
( only terrify the dolts, And to him    )
( who's scientific There is nothing     )
( that's terrific In the pattern of a   )
( flight of thunderbolts!               )
(                                       )
( -- W.S. Gilbert, "The Mikado"         )
 ---------------------------------------
o                             .       .
 o                           / `.   .' "
  o                  .---.  <    > <    >  .---.
   o                 |    \  \ - ~ ~ - /  /    |
         _____          ..-~             ~-..-~
        |     |   \~~~\.'                    `./~~~/
       ---------   \__/                        \__/
      .'  O    \     /               /       \  "
     (_____,    `._.'               |         }  \/~~~/
      `----.          /       }     |        /    \__/
            `-.      |       /      |       /      `. ,~~|
                ~-.__|      /_ - ~ ^|      /- _      `..-'
                     |     /        |     /     ~-.     `-. _  _  _
                     |_____|        |_____|         ~ - . _ _ _ _ _>

# 两个包有依赖，要同时卸载？
$ pacman -U /var/cache/pacman/pkg/virtualbox-guest-utils-4.3.20-1-x86_64.pkg.tar.xz /var/cache/pacman/pkg/xorg-server-1.16.3-2-x86_64.pkg.tar.xz
$ pacman -U /var/cache/pacman/pkg/xf86-video-modesetting-0.9.0-2-x86_64.pkg.tar.xz

IgnorePkg = virtualbox xorg-server

import numpy as np
import matplotlib.pylab as plt
def mse(n):
    return 20 * np.log10(255.0/n)
x, xx = np.linspace(0.1, 10, 100), np.linspace(1, 10, 10)
y, yy = mse(x), mse(xx)
plt.plot(x, y, xx, yy, "r*")
plt.xlabel("MSE")
plt.ylabel("PSNR(dB)")
plt.grid(True)
plt.show()

$ python -m timeit -n 1 -r 10 "import myfun.py; myfun.foo()"

rfc(){ gvim /usr/share/doc/rfc/txt/$1.txt }