python - 为什么 flask url_for 太慢

Question

我用这段代码测试了它:

from gevent import wsgi, monkey; monkey.patch_all()
from flask import Flask, url_for

app = Flask(__name__)

@app.route('/<int:n>')
def index(n):
    for i in xrange(n):
        url = url_for('index', n=i)
    return url 

wsgi.WSGIServer(('', 8000), app).serve_forever()

结果:

• /1 每秒请求数:2721.94 [#/sec](平均值)
• /10 每秒请求数:1080.16 [#/sec](平均值)
• /100 每秒请求数:144.66 [#/sec](平均值)

Answer 1

确实有点慢。

好消息是时间复杂度是线性的，O(1)。

下面是cProfile转储

如果我是 Flask 开发人员，我会看看为什么 url_for 会同时调用 urljoin 和 urlsplit。如果我正确理解 werkzeug 代码，它会对生成的 url 执行验证。

         13726316 function calls (13526316 primitive calls) in 16.918 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
   400000    0.272    0.000    0.453    0.000 <string>:8(__new__)
   100000    0.120    0.000    0.140    0.000 app.py:1484(inject_url_defaults)
   200000    0.762    0.000    1.052    0.000 datastructures.py:316(__init__)
   100000    0.132    0.000    0.395    0.000 globals.py:16(_lookup_object)
   100000    0.913    0.000   16.996    0.000 helpers.py:250(url_for)
   300000    0.527    0.000    0.846    0.000 local.py:156(top)
   100000    0.136    0.000    0.645    0.000 local.py:289(_get_current_object)
   100000    0.112    0.000    0.901    0.000 local.py:333(__getattr__)
   300000    0.264    0.000    0.320    0.000 local.py:66(__getattr__)
   200000    0.059    0.000    0.059    0.000 routing.py:1199(update)
   200000    0.147    0.000    0.147    0.000 routing.py:1455(get_host)
400000/200000    0.802    0.000    6.297    0.000 routing.py:1520(_partial_build)
   200000    1.791    0.000   14.382    0.000 routing.py:1541(build)
   400000    0.153    0.000    0.153    0.000 routing.py:1601(<genexpr>)
   200000    1.830    0.000    5.181    0.000 routing.py:701(build)
   200000    0.275    0.000    0.275    0.000 routing.py:743(suitable_for)
   200000    0.256    0.000    0.256    0.000 routing.py:928(to_url)
   400000    0.935    0.000    2.816    0.000 urlparse.py:128(urlparse)
   400000    1.010    0.000    1.428    0.000 urlparse.py:159(urlsplit)
   200000    0.175    0.000    0.274    0.000 urlparse.py:214(urlunparse)
   200000    0.099    0.000    0.099    0.000 urlparse.py:224(urlunsplit)
   200000    1.961    0.000    5.637    0.000 urlparse.py:242(urljoin)
     5263    0.004    0.000    0.019    0.000 urlparse.py:62(clear_cache)
   400000    0.483    0.000    0.783    0.000 urls.py:36(_quote)
   400000    0.509    0.000    1.534    0.000 urls.py:369(url_quote)
   100000    0.068    0.000    0.068    0.000 wrappers.py:85(blueprint)
   505263    0.235    0.000    0.235    0.000 {built-in method __new__ of type object at 0x10d044248}
   200000    0.101    0.000    0.169    0.000 {getattr}
   100000    0.114    0.000    0.114    0.000 {hasattr}
  2000000    0.642    0.000    0.642    0.000 {isinstance}
   505263    0.073    0.000    0.073    0.000 {len}
   200000    0.041    0.000    0.041    0.000 {method 'add' of 'set' objects}
   600000    0.127    0.000    0.127    0.000 {method 'append' of 'list' objects}
     5263    0.015    0.000    0.015    0.000 {method 'clear' of 'dict' objects}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
     5263    0.003    0.000    0.003    0.000 {method 'find' of 'str' objects}
   100000    0.072    0.000    0.072    0.000 {method 'find' of 'unicode' objects}
   700000    0.231    0.000    0.231    0.000 {method 'get' of 'dict' objects}
   400000    0.105    0.000    0.105    0.000 {method 'iteritems' of 'dict' objects}
   200000    0.116    0.000    0.116    0.000 {method 'join' of 'str' objects}
   200000    0.157    0.000    0.157    0.000 {method 'join' of 'unicode' objects}
   200000    0.134    0.000    0.134    0.000 {method 'lstrip' of 'unicode' objects}
   300000    0.052    0.000    0.052    0.000 {method 'pop' of 'dict' objects}
   200000    0.079    0.000    0.079    0.000 {method 'remove' of 'list' objects}
   400000    0.249    0.000    0.249    0.000 {method 'rstrip' of 'str' objects}
   200000    0.183    0.000    0.183    0.000 {method 'split' of 'str' objects}
   400000    0.339    0.000    0.339    0.000 {method 'split' of 'unicode' objects}
   300000    0.056    0.000    0.056    0.000 {thread.get_ident}

我有 2-3 个实用的解决方案:

• 缓存(最常见的)url_for 结果
• 将 url_for 计算卸载到客户端/js
• 硬编码 url 生成

如果您有带数字 ID 的 RESTful API，最后一个选项可能如下所示:

datum_url_template = url_for("datum", n=999)
def url_for_datum(n):
    return datum_url_template.replace("999", str(n))

foobar_url_template = url_for("foobar", n=777)
def url_for_foobar(n):
    return foobar_url_template.replace("777", str(n))