项目访问时间：设置v。列表 [英] item access time: sets v. lists
问题描述
对访问set元素的期望是否比访问list元素要慢得多？b $ b？说明？
谢谢，
Alan Isaac
>> t1 = timeit.Timer（&for; for i in set（xrange（10000））：pass"，""）
t2 = timeit.Timer（" for i in list（xrange（10000））：pass"，""）
t1.timeit（1000）
9.806250235714316
>> t2.timeit（1000）
3.9823075279120701
2006年10月4日星期三16:02:56 GMT
David Isaac < ai ***** @ verizon.netwrote：
预期对设置元素的访问要比
慢吗？访问列表元素？说明？
谢谢，
Alan Isaac
> t1 = timeit.Timer（" for i in set（xrange（10000））：pass，，）
t2 = timeit.Timer（" for i in list（xrange（10000））：pass" ，"）
[...]
你''重新测量创建xrange和set / list的时间。
在调用Timer（）之前创建它们并重复你的时间。
Dennis Benzinger
" David Isaac" < ai ***** @ verizon.netwrote in message
news：QWQUg.15396
3T2.2982@trnddc06 ...
访问set元素是否比访问list元素要慢得多？b $ b？说明？
谢谢，
Alan Isaac
>> > t1 = timeit.Timer（&for; for i in set（xrange（10000））：pass"，""）
t2 = timeit.Timer（" for i in list（xrange（10000）） ）：传递"，""）
t1.timeit（1000）
9.806250235714316
>>> t2.timeit（1000）
3.9823075279120701
几点：
1.你对timeit的使用有点瑕疵。您不仅可以将访问权限计入集合或列表，还可以构建集合/列表，*每个
时间*。使用第二个字符串arg（你要传递的那个作为"）来进行一次性初始化，这样你只能测量访问权限，这就是你的b
说你有兴趣。
2.哎呀，事实证明你并没有真正*访问*设置/列表，你是
*迭代*在它上面。鉴于这些集合是使用
树结构在内部实现的，我希望迭代列表可能会更快，
尽管只是略微如此。
3.以下是一些更正确的时间统计数据：
构造列表/设置
设置-1.89524618352
清单-0.299499796762
迭代列表/设置
set -0.646887523414
list -0.552001162159
随机访问列表/集中的第一项
set -0.000189409547861
list -0.000160076210804
随机访问项目存在时列表/设置项目
set -0.000241650824337
list -0.0245168031132
随机访问列表/集合中的项目当项目不存在时
set -0.000187733357172
list -0.522086186932
代码：
import timeit
print" \\\
Construct list / set"
t1 = timeit.Timer（" z = set（xrange（10000））"，""）
t2 = timeit.Timer（" z = list（xrange（10000））"，""）
print" set - >"，t1.timeit（1000）
print" list - >"，t2.timeit（1000）
print" \\\
Iterate over list / set"
t1 = timeit.Timer（" for i in z：pass"，" z = set （xrange（10000））"）
t2 = timeit.Timer（" for i in z：pass"，" z = list（xrange（10000））"）
print" set - >"，t1.timeit（1000）
print" list - >"，t2.timeit（1000）
print" \ nandand访问list / set中的第一项"
t1 = timeit.Timer（" 0 in z"，" z = set（xrange） （10000））"）
t2 = timeit.Timer（" 0 in z"，" z = list（xrange（10000））"）
print" set - >"，t1.timeit（1000）
print" list - >"，t2.timeit（1000）
打印" \ nR当项目存在时，andom访问列表/集合中的项目
t1 = timeit.Timer（" 500 in z"，" z = set（xrange（10000））"）
t2 = timeit.Timer（" 500 in z"，" z = list（xrange（10000））"）
print" set - >"， t1.timeit（1000）
打印" list - >"，t2.timeit（1000）
print" \ nandand访问权限列表中的项目/当项目不存在时设置
t1 = timeit.Timer（" 10500 in z，z = set（xrange（10000）））
t2 = timeit.Timer（" 10500 in z"，" z = list（xrange（10000））"）
print" set - >"，t1 .timeit（1000）
打印" list - >"，t2.timeit（1000）
- Paul
Is it expected for access to set elements to be much
slower than access to list elements? Explanation?
Thanks,
Alan Isaac
>>t1=timeit.Timer("for i in set(xrange(10000)):pass","")
t2=timeit.Timer("for i in list(xrange(10000)):pass","")
t1.timeit(1000)
9.806250235714316
>>t2.timeit(1000)
3.9823075279120701
On Wed, 04 Oct 2006 16:02:56 GMT
"David Isaac" <ai*****@verizon.netwrote:
Is it expected for access to set elements to be much
slower than access to list elements? Explanation?
Thanks,
Alan Isaac
>t1=timeit.Timer("for i in set(xrange(10000)):pass","")
t2=timeit.Timer("for i in list(xrange(10000)):pass","")
[...]
You''re measuring the time for creating the xrange and the set/list too.
Create them before you call Timer() and repeat your timing.
Dennis Benzinger
"David Isaac" <ai*****@verizon.netwrote in message
news:QWQUg.15396
3T2.2982@trnddc06...Is it expected for access to set elements to be much
slower than access to list elements? Explanation?
Thanks,
Alan Isaac
>>>t1=timeit.Timer("for i in set(xrange(10000)):pass","")
t2=timeit.Timer("for i in list(xrange(10000)):pass","")
t1.timeit(1000)
9.806250235714316
>>>t2.timeit(1000)
3.9823075279120701
A couple of points:
1. Your use of timeit is a bit flawed. You are not only timing the access
into the set or list, but also the construction of the set/list, *every
time*. Use the second string arg (the one you are passing as "") for
one-time initialization, so that you measure only access, which is what you
say your are interested in.
2. Ooops, it turns out you''re not really *accessing* the set/list, you are
*iterating* over it. Given that sets are implemented internally using a
tree structure, I would expect that iterating over a list could be faster,
although only marginally so.
3. Here are some stats for a little more correct timeits:
Construct list/set
set -1.89524618352
list -0.299499796762
Iterate over list/set
set -0.646887523414
list -0.552001162159
Random access to first item in list/set
set -0.000189409547861
list -0.000160076210804
Random access to item in list/set when item exists
set -0.000241650824337
list -0.0245168031132
Random access to item in list/set when item does not exist
set -0.000187733357172
list -0.522086186932
The code:
import timeit
print "\nConstruct list/set"
t1=timeit.Timer("z = set(xrange(10000))","")
t2=timeit.Timer("z = list(xrange(10000))","")
print "set ->", t1.timeit(1000)
print "list ->", t2.timeit(1000)
print "\nIterate over list/set"
t1=timeit.Timer("for i in z: pass","z = set(xrange(10000))")
t2=timeit.Timer("for i in z: pass", "z = list(xrange(10000))")
print "set ->", t1.timeit(1000)
print "list ->", t2.timeit(1000)
print "\nRandom access to first item in list/set"
t1=timeit.Timer("0 in z","z = set(xrange(10000))")
t2=timeit.Timer("0 in z", "z = list(xrange(10000))")
print "set ->", t1.timeit(1000)
print "list ->", t2.timeit(1000)
print "\nRandom access to item in list/set when item exists"
t1=timeit.Timer("500 in z","z = set(xrange(10000))")
t2=timeit.Timer("500 in z", "z = list(xrange(10000))")
print "set ->", t1.timeit(1000)
print "list ->", t2.timeit(1000)
print "\nRandom access to item in list/set when item does not exist"
t1=timeit.Timer("10500 in z","z = set(xrange(10000))")
t2=timeit.Timer("10500 in z", "z = list(xrange(10000))")
print "set ->", t1.timeit(1000)
print "list ->", t2.timeit(1000)
-- Paul
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