总是忘记，做个记录。
性能定义
一般而言，处理一个请求的速度是一个重要的性能指标（Latency， 系统延迟）。
观察工具
有时候不需要特殊工具，直接看一个http请求的时长即可。
定位瓶颈
line_profiler是一个可以查看每行代码的执行次数、执行时间的工具。
安装好后，可以在代码中对方法/函数添加装饰器@profile，然后在命令行使用kernprof -l -v xx.py来查看结果。
这样太麻烦，可以直接在IPython中直接使用。
导入：
In [1]: %load_ext line_profiler
help：
In [2]: %lprun?
Docstring:
Execute a statement under the line-by-line profiler from the
line_profiler module.
Usage:
%lprun -f func1 -f func2 <statement>
The given statement (which doesn't require quote marks) is run via the
LineProfiler. Profiling is enabled for the functions specified by the -f
options. The statistics will be shown side-by-side with the code through the
pager once the statement has completed.
Options:
-f <function>: LineProfiler only profiles functions and methods it is told
to profile. This option tells the profiler about these functions. Multiple
-f options may be used. The argument may be any expression that gives
a Python function or method object. However, one must be careful to avoid
spaces that may confuse the option parser. Additionally, functions defined
in the interpreter at the In[] prompt or via %run currently cannot be
displayed. Write these functions out to a separate file and import them.
-m <module>: Get all the functions/methods in a module
One or more -f or -m options are required to get any useful results.
-D <filename>: dump the raw statistics out to a pickle file on disk. The
usual extension for this is ".lprof". These statistics may be viewed later
by running line_profiler.py as a script.
-T <filename>: dump the text-formatted statistics with the code side-by-side
out to a text file.
-r: return the LineProfiler object after it has completed profiling.
-s: strip out all entries from the print-out that have zeros.
File: /Library/Python/2.7/site-packages/line_profiler.py
举例：
在exmaple.py中：
class Demo:
def method1(self):
self.method2()
def method2(self):
pass
也可直接使用IPython的%%writefile来直接写一个。
查看运行情况，其中每个-f后都可加一个函数/方法，用于执行情况。
from example import Demo
demo = Demo()
%lprun -f demo.method1 demo.method1()
%lprun -f demo.method1 -f demo.method2 demo.method1()
这样就能找到瓶颈啦！
