# 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：
* `Line magics`：`%`，只接受该行的参数
* `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。
这些都等同于`%% script <name>`
```
%%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" >&2
```
```
hi, stdout
hello, stderr
```
```
%%bash --out output --err error
echo "hi, stdout"
echo "hello, stderr" >&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 "<ipython-input-22-133f42941cdb>", line 1, in <module>
f2(1)
File "<ipython-input-20-05ec2e2678a0>", line 6, in f2
return f1(a,b)
File "<ipython-input-20-05ec2e2678a0>", 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)
<ipython-input-24-133f42941cdb> in <module>()
----> 1 f2(1)
global f2 = <function f2 at 0x0C334CB0>
<ipython-input-20-05ec2e2678a0> in f2(x=1)
4 a = x
5 b = x-1
----> 6 return f1(a,b)
global f1 = <function f1 at 0x0C334CF0>
a = 1
b = 0
<ipython-input-20-05ec2e2678a0> in f1(a=1, b=0)
1 def f1(a,b):
----> 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<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 <string>:2(fib)
1 0.000 0.000 0.009 0.009 <string>:2(<module>)
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/)