csdn_spider/blog/ds19991999/原创-- 02-Ipython Magic魔术.md

# 原创
：  02-Ipython Magic魔术

# 02-Ipython Magic魔术

## IPython Magic 魔术

具体见个人Python图书馆：[https://ds-ebooks.github.io](https://ds-ebooks.github.io)

### 简介

两种`magic`命令： <br/> * `Line magics`：`%`，只接受该行的参数 <br/> * `Cell magics`: `%%`，只能用在`cell`首行，`%%`接收的`magic`参数包括整个`cell`，并且每个单元格只能用一个`cell`

```
# 列出可用的魔法命令
%lsmagic
```

```
Available line magics:
%alias  %alias_magic  %autocall  %automagic  %autosave  %bookmark  %cd  %clear  %cls  %colors  %config  %connect_info  %copy  %ddir  %debug  %dhist  %dirs  %doctest_mode  %echo  %ed  %edit  %env  %gui  %hist  %history  %killbgscripts  %ldir  %less  %load  %load_ext  %loadpy  %logoff  %logon  %logstart  %logstate  %logstop  %ls  %lsmagic  %macro  %magic  %matplotlib  %mkdir  %more  %notebook  %page  %pastebin  %pdb  %pdef  %pdoc  %pfile  %pinfo  %pinfo2  %popd  %pprint  %precision  %profile  %prun  %psearch  %psource  %pushd  %pwd  %pycat  %pylab  %qtconsole  %quickref  %recall  %rehashx  %reload_ext  %ren  %rep  %rerun  %reset  %reset_selective  %rmdir  %run  %save  %sc  %set_env  %store  %sx  %system  %tb  %time  %timeit  %unalias  %unload_ext  %who  %who_ls  %whos  %xdel  %xmode

Available cell magics:
%%!  %%HTML  %%SVG  %%bash  %%capture  %%cmd  %%debug  %%file  %%html  %%javascript  %%js  %%latex  %%perl  %%prun  %%pypy  %%python  %%python2  %%python3  %%ruby  %%script  %%sh  %%svg  %%sx  %%system  %%time  %%timeit  %%writefile

Automagic is ON, % prefix IS NOT needed for line magics.

```

### 简单`Magic`

```
%matplotlib inline
import numpy as np 
import matplotlib.pyplot as plt
```

```
# %timeit计算代码执行时间
%timeit np.linalg.eigvals(np.random.rand(100,100))
```

```
100 loops, best of 3: 7.31 ms per loop

```

#### 计算整个`cell` 代码运行时间

```
%%timeit a = np.random.rand(100, 100)
np.linalg.eigvals(a)
```

```
100 loops, best of 3: 6.98 ms per loop

```

#### `%%capture`捕获`cell`输出`stdout/stderr`

```
%%capture capt
from __future__ import print_function
import sys
print('Hello stdout')
print('and stderr', file=sys.stderr)
```

```
capt.stdout,capt.stderr
```

```
('Hello stdout\n', 'and stderr\n')

```

```
capt.show()
```

```
Hello stdout


and stderr

```

#### `%%capture result`有同样的功能

```
%%capture result

print([1,2,3])
```

```
result.stdout
```

```
'[1, 2, 3]\n'

```

```
result.show()
```

```
[1, 2, 3]

```

#### `%%scipy cell magic`

```
%%script python
import sys
print 'hello from Python %s' % sys.version
```

```
hello from Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:42:59) [MSC v.1500 32 bit (Intel)]

```

```
%%script python3
import sys
print('hello from Python: %s' % sys.version)
```

```
hello from Python: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 17:26:49) [MSC v.1900 32 bit (Intel)]

```

`IPython`还为一些常见的解释器创建别名，例如`bash，ruby，perl`等。 <br/> 这些都等同于`%% script &lt;name&gt;`

```
%%bash
echo "hello from $BASH"
```

```
hello from /usr/bin/bash

```

#### `--out` `--err`捕获`cell`魔法的输出

```
%%bash
echo "hi, stdout"
echo "hello, stderr" &gt;&amp;2
```

```
hi, stdout


hello, stderr

```

```
%%bash --out output --err error
echo "hi, stdout"
echo "hello, stderr" &gt;&amp;2
```

```
print(error)
print(output)
```

```
hello, stderr

hi, stdout

```

```
%matplotlib inline
import pylab as pl
pl.seed(1)
data = pl.randn(100)
pl.plot(data);
```

#### 配合 `%config InlineBackend.figure_format="svg"`做图片输出格式的设置

```
%config InlineBackend.figure_format="svg"
%matplotlib inline
```

```
pl.plot(data);
```

#### 调试代码的模式 `%xmode Plain`和原来的模式`%xmode Verbose`

```
def f1(a,b):
    return a/b
def f2(x):
    a = x
    b = x-1
    return f1(a,b)
```

```
# 精简模式
%xmode Plain
```

```
Exception reporting mode: Plain

```

```
f2(1)
```

```
Traceback (most recent call last):


  File "&lt;ipython-input-22-133f42941cdb&gt;", line 1, in &lt;module&gt;
    f2(1)


  File "&lt;ipython-input-20-05ec2e2678a0&gt;", line 6, in f2
    return f1(a,b)


  File "&lt;ipython-input-20-05ec2e2678a0&gt;", line 2, in f1
    return a/b


ZeroDivisionError: integer division or modulo by zero

```

```
# 原来的模式
%xmode Verbose
```

```
Exception reporting mode: Verbose

```

```
f2(1)
```

```
ZeroDivisionErrorTraceback (most recent call last)

&lt;ipython-input-24-133f42941cdb&gt; in &lt;module&gt;()
----&gt; 1 f2(1)
        global f2 = &lt;function f2 at 0x0C334CB0&gt;


&lt;ipython-input-20-05ec2e2678a0&gt; in f2(x=1)
      4     a = x
      5     b = x-1
----&gt; 6     return f1(a,b)
        global f1 = &lt;function f1 at 0x0C334CF0&gt;
        a = 1
        b = 0


&lt;ipython-input-20-05ec2e2678a0&gt; in f1(a=1, b=0)
      1 def f1(a,b):
----&gt; 2     return a/b
        a = 1
        b = 0
      3 def f2(x):
      4     a = x
      5     b = x-1


ZeroDivisionError: integer division or modulo by zero

```

#### `%debug`用户调试错误

使用`%debug`会在报错时进去调试模式,在调试模式中我们可以

#### `%timeit`和`%time`

```
%timeit sum(map(lambda x:x**2,range(100)))
```

```
10000 loops, best of 3: 18.5 µs per loop

```

```
%time sum(map(lambda x:x**2,range(100)))
```

```
Wall time: 0 ns





328350

```

#### `%%prun/%prun`命令调用`profile`模块，对单元中的代码进行宏观上的性能剖析

```
%%prun
def fib(n):
    if n&lt;2:
        return n
    return fib(n-1)+fib(n-2)
fib(20)
```

像这样：

```
         21893 function calls (3 primitive calls) in 0.009 seconds

   Ordered by: internal time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
  21891/1    0.009    0.000    0.009    0.009 &lt;string&gt;:2(fib)
        1    0.000    0.000    0.009    0.009 &lt;string&gt;:2(&lt;module&gt;)
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
```

### 参考资料

[Jupyter攻略](http://blog.hszofficial.site/TutorialForJupyter/)