%pylab的意思

%pylab的意思

一、总结

一句话总结：

【Load numpy and matplotlib to work interactively.】

【activate pylab】：This function lets you activate pylab (matplotlib, numpy and interactive support) at any point during an IPython session.

%pylab makes the following imports:

import numpy
import matplotlib
from matplotlib import pylab, mlab, pyplot
np = numpy
plt = pyplot

from IPython.display import display
from IPython.core.pylabtools import figsize, getfigs

from pylab import *
from numpy import *

1、how magic functions work in python？

【%ls】：to view cwd directory contents

【begin with the percent sign (%)】：Magic functions in ipython always begin with the percent sign (%) followed without any spaces by a small text string

【define shortcuts particularly useful for interactive work】：in essence, ipython magic functions define shortcuts particularly useful for interactive work

二、%pylab的意思

转自或参考：

%pylab 是 IPython 中的一个 magic 函数。可以查看代码中 import 了哪些包。

%pylab是IPython中的一个 magic函数。可以查看代码中 import 了哪些包。通过 ipython notebook --pylab inline, 可以让 plot 出来的图片直接嵌入在notebook里面 ^[1]  。

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answer one：

%pylab is a magic function in ipython.

Magic functions in ipython always begin with the percent sign (%) followed without any spaces by a small text string; in essence, ipython magic functions define shortcuts particularly useful for interactive work, e.g., to give you an idea of how magic functions work in python, a few of my favorites:

• to view cwd directory contents:

  %ls   
  

• to run a script in ipython using an empty namespace, type space then a script name:

  %run     
  

• to execute a code snippet (particularly for multi-line snippets which would usually cause an _IndentationError_ to be thrown):

  %paste
  

When the %pylab magic function is entered at the IPython prompt, it triggers the import of various modules within Matplotlib.

Which modules? well, the ones subsumed under the pylab interface.

The awesome Matplotlib plotting library has two distinct interfaces: a pythonic one, and the original MATLAB-like one intended for plotting at the interactive prompt.

The former is usually imported like so:

from matplotlib import pyplot as PLT

Indeed, pyplot has its own magic python magic function

%pyplot

Why two different interfaces? Matplotlib's original interface was pylab; only later was the pythonic interface added. Scripting and app development were not the primary uses cases for Matplotlib when the project began, plotting in the python shell was.

Apparently John Hunter (Matplotlib's creator) wanted to include interactive plotting in python so he submitted a patch to Fernando Perez's (FP) IPython project. FP was a Ph.D student at the time and informed JH that he would not able to review the path for some time. As a result, JH created Matplotlib. The significance is that Matplotlib began as a shell-based plotting scheme.

the pylab interface is indeed more suitable for interactive work:

from pylab import *

x, y = arange(10), cos(x/2)
plot(x, y)
show()

and using the pyplot interface:

from matplotlib import pyplot as PLT
import numpy as NP

x, y = NP.arange(10), NP.cos(x/2)
fig = PLT.figure()
ax1 = fig.add_subplot(111)
ax1.plot(x, y)
PLT.show()

 

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answer two：

%pylab is shortcut for typing all of below commands which in essence adds numpy and matplotlib in to your session. This was added in IPython as a transition tool and current recommendation is that you should not use it. The core reason is that below sets of commands imports too much in the global namespace and also it doesn't allow you to change the mode for matplotlib from UI to QT or something else. You can get history and reasoning behind this at http://nbviewer.ipython.org/github/Carreau/posts/blob/master/10-No-PyLab-Thanks.ipynb?create=1.

This is what %pylab does:

import numpy
import matplotlib
from matplotlib import pylab, mlab, pyplot
np = numpy
plt = pyplot

from IPython.core.pylabtools import figsize, getfigs

from pylab import *
from numpy import *

This is what I use instead at the start of my notebook:

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

 

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answer three：

%pylab

%pylab [--no-import-all] [gui]

Load numpy and matplotlib to work interactively.

This function lets you activate pylab (matplotlib, numpy and interactive support) at any point during an IPython session.

%pylab makes the following imports:

import numpy
import matplotlib
from matplotlib import pylab, mlab, pyplot
np = numpy
plt = pyplot

from IPython.display import display
from IPython.core.pylabtools import figsize, getfigs

from pylab import *
from numpy import *

If you pass --no-import-all, the last two * imports will be excluded.

See the %matplotlib magic for more details about activating matplotlib without affecting the interactive namespace.

positional arguments:

gui Name of the matplotlib backend to use (‘gtk’, ‘gtk3’,

‘inline’, ‘nbagg’, ‘notebook’, ‘osx’, ‘qt’, ‘qt4’, ‘qt5’, ‘tk’, ‘wx’). If given, the corresponding matplotlib backend is used, otherwise it will be matplotlib’s default (which you can set in your matplotlib config file).

optional arguments:

--no-import-all
	Prevent IPython from performing import * into the interactive namespace. You can govern the default behavior of this flag with the InteractiveShellApp.pylab_import_all configurable.

 

 

 

 

参考：

https://baike.baidu.com/item/pylab/20436252?fr=aladdin

https://stackoverflow.com/questions/20961287/what-is-pylab

https://ipython.org/ipython-doc/dev/interactive/magics.html