5.4.2. 魔法命令 [3]¶
There are two kinds of magics, line-oriented and cell-oriented:
1. Line magics:
prefixed with the % character and work much like OS command-line calls
2. Cell magics:
prefixed with a double %%, and they are functions
that get as an argument not only the rest of the line,
but also the lines below it in a separate argument.
实例:
In [1]: %timeit range(1000)
100000 loops, best of 3: 7.76 us per loop
In [2]: %%timeit x = range(10000)
...: max(x)
...:
1000 loops, best of 3: 223 us per loop
The built-in magics include:
Functions that work with code: %run, %edit, %save, %macro, %recall, etc.
Functions which affect the shell: %colors, %xmode, %automagic, etc.
Other functions such as %reset, %timeit, %%writefile, %load, or %paste.
时间相关:
%timeit: 命令快速测量代码运行时间
In [33]: %timeit range(1000)
195 ns ± 23.1 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
# 注意前提: import np等
In [34]: %%timeit a = np.random.rand(100, 100)
...: np.linalg.eigvals(a)
...:
...:
195 ns ± 23.1 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%%capture打印相关:
In [24]: %%capture capt
...: from __future__ import print_function
...: import sys
...: print('Hello stdout')
...: print('and stderr', file=sys.stderr)
...:
...:
In [25]: capt.stdout, capt.stderr
...:
Out[25]: ('Hello stdout\n', 'and stderr\n')
In [27]: capt.show()
...:
Hello stdout
and stderr
%%writefile写文件相关:
In [29]: %%writefile foo123.py
...: print('Hello world')
...:
...:
In [36]: %run foo123
Hello world
%lsmagic查看所有的「魔法命令」:
In [1]: %lsmagic
%bg命令:
In [1]: %bg function: 把function放到后台执行，例如:
In [1]: %bg myfunc(x, y,z=1)
之后可以用jobs将其结果取回
myvar = jobs.result(5) 或 myvar =jobs[5].result
另外:jobs.status() 可以查看现有任务的状态。
Background Scripts:
实例:
In [47]: %%ruby --bg --out ruby_lines
...: for n in 1...10
...: sleep 1
...: puts "line #{n}"
...: STDOUT.flush
...: end
...:
...:
In [48]: ruby_lines
Out[48]: <_io.BufferedReader name=73>
In [49]: print(ruby_lines.read().decode('utf8'))
...:
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
Arguments to subcommand:
In [51]: %%script python2 -Qnew
...: print 1/3
...:
...:
0.333333333333
In [50]: %%script --bg --out bashout bash -c "while read line; do echo $line; sleep 1; done"
...: line 1
...: line 2
...: line 3
...: line 4
...: line 5
...:
...:
In [52]: import time
...: tic = time.time()
...: line = True
...: while True:
...: line = bashout.readline()
...: if not line:
...: break
...: sys.stdout.write("%.1fs: %s" %(time.time()-tic, line))
...: sys.stdout.flush()
...:
0.0s: b'line 1\n'0.0s: b'line 2\n'0.0s: b'line 3\n'0.0s: b'line 4\n'0.0s: b'line 5\n'0.0s: b'\n'
%edit编辑命令:
%ed或%edit编辑一个文件并执行
如果只编辑不执行，用 ed -x filename 即可。
%run命令运行脚本:
作用:
allows you to run any python script and load all of its data directly into the interactive namespace
special flags:
1. (-t): timing the execution of your scripts
2. (-d): Python’s pdb debugger
3. (-p): Python’s profiler
实例:
In [1]: %run ../utils/list_pyfiles.ipy
%debug:
jump into the Python debugger (pdb) and examine the problem
%pdb:
IPython will automatically start the debugger on any uncaught exception
%matplotlib:
Set up matplotlib to work interactively.
1. %matplotlib
使用default matplotlib backend in a separate window
2. %matplotlib inline
Available only for the Jupyter Notebook and the Jupyter QtConsole.
3. 指定使用某backend
%matplotlib gtk # 指定使用gtk
%matplotlib qt
%matplotlib TkAgg
// You can list the available backends using the -l/--list option:
%matplotlib --list
Available matplotlib backends: ['osx', 'qt4', 'qt5', 'gtk3', 'notebook', 'wx', 'qt', 'nbagg',
'gtk', 'tk', 'inline']
System shell commands:
! 表示执行shell命令
如:
!ping www.bbc.co.uk
$将python的变量转化成shell变量
帮助命令:
%<Cmd>?
如:
%matplotlib?
%script命令:
In [38]: %%script python2
...: import sys
...: print 'hello from Python %s' % sys.version
...:
...:
hello from Python 2.7.16 (default, Dec 13 2019, 18:00:32)
[GCC 4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.32.4) (-macos10.15-objc-s
In [39]: %%script python3
...: import sys
...: print('hello from Python: %s' % sys.version)
...:
...:
hello from Python: 3.7.6 (default, Jan 8 2020, 13:42:34)
[Clang 4.0.1 (tags/RELEASE_401/final)]
In [40]: %%ruby # alias of `script ruby`
...: puts "Hello from Ruby #{RUBY_VERSION}"
...:
...:
Hello from Ruby 2.6.3
In [41]: %%bash # alias of `script bash`
...: echo "hello from $BASH"
...:
...:
hello from /bin/bash
%%bash命令:
In [43]: %%bash
...: echo "hi, stdout"
...: echo "hello, stderr" >&2
...:
...:
hi, stdout
hello, stderr
In [44]: %%bash --out output --err error
...: echo "hi, stdout"
...: echo "hello, stderr" >&2
...:
...:
In [45]: print(error)
...:
hello, stderr
In [46]: print(output)
hi, stdout
其他:
%env显示环境变量。
%hist或%history显示历史记录。
%macro name n1-n2 n3-n4 ... n5 .. n6 ...创建一个名称为name的宏，执行name就是执行n1-n2 n3-n4 ... n5 .. n6 ...这些代码。
%pwd显示当前目录
%pycat filename用语法高亮显示一个python文件（不用加.py后缀名）。
%save filename n1-n2 n3-n4 ... n5 .. n6 ...将执行过多代码保存为文件
%debug命令在异常点启动调试器。
%pdb命令来激活IPython调试器，这样，每当异常抛出时，调试器就会自动运行。
%pylab命令可以使Numpy和matplotlib中的科学计算功能生效。