blocks|key|1573549|text|它可能只是请求操作系统提供的函数，而不是它自己的算法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1573550|正如其他评论所说，使用hashlib或编写自己的散列函数。|offset|length|1573551|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/hashlib.html?highlight=hash#module-hashlib^0|0|B|7|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

It probably just asks the operating system provided function, rather than its own algorithm. 

As other comments says, use <a href="http://docs.python.org/library/hashlib.html?highlight=hash#module-hashlib" rel="nofollow noreferrer">hashlib</a> or write your own hash function.

blocks|key|1358350|text|据猜测，AppEngine使用的是Python64位实现(-5768830964305142685不适合32位)，而您的Python实现是32位。你不能指望对象散列在不同的实现之间是有意义的比较。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1358351|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

At a guess, AppEngine is using a 64-bit implementation of Python (-5768830964305142685 won't fit in 32 bits) and your implementation of Python is 32 bits. You can't rely on object hashes being meaningfully comparable between different implementations.

blocks|key|1573682|text|散列结果在32位和64位平台之间有所不同|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1573683|如果计算出的哈希在两个平台上都相同，请考虑使用|1573684|def+hash32(value):
++++return+hash(value)+&+0xffffffff|code-block|syntax|javascript|1573685|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Hash results varies between 32bit and 64bit platforms

If a calculated hash shall be the same on both platforms consider using

<pre><code>def hash32(value):
 return hash(value) &amp; 0xffffffff
</code></pre>

blocks|key|1573743|text|那么sign+bit呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1573744|例如：|1573745|十六进制值0xADFE74A5表示无符号2919134373和有符号-1375832923。Currect值必须是有符号的(sign+bit+=+1)，但是python将其转换为无符号的，并且在从64位转换为32位后，我们有一个不正确的哈希值。|offset|length|style|CODE|1573746|请谨慎使用：|1573747|def+hash32(value):
++++return+hash(value)+&+0xffffffff|code-block|syntax|javascript|1573748|entityMap^0|0|0|5|A|K|A|Y|B|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@$F|V|G|W|H|I]|$F|X|G|Y|H|I]|$F|Z|G|10|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|11|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|12|8|@]|9|@]|A|$O|P]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

What about sign bit?

For example:

Hex value <code>0xADFE74A5</code> represents unsigned <code>2919134373</code> and signed <code>-1375832923</code>.
Currect value must be signed (sign bit = 1) but python converts it as unsigned and we have an incorrect hash value after translation from 64 to 32 bit.

Be careful using:

<pre><code>def hash32(value):
 return hash(value) &amp; 0xffffffff
</code></pre>

blocks|key|1358524|text|这是Google在python+2.5的生产中使用的散列函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1358525|def+c_mul(a,+b):
++return+eval(hex((long(a)+*+b)+&+(2**64+-+1))[:-1])

def+py25hash(self):
++if+not+self:
++++return+0+#+empty
++value+=+ord(self[0])+<<+7
++for+char+in+self:
++++value+=+c_mul(1000003,+value)+%5E+ord(char)
++value+=+value+%5E+len(self)
++if+value+==+-1:
++++value+=+-2
++if+value+>=+2**63:
++++value+-=+2**64
++return+value|code-block|syntax|javascript|1358526|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is the hash function that Google uses in production for python 2.5:

<pre><code>def c_mul(a, b):
 return eval(hex((long(a) * b) &amp; (2**64 - 1))[:-1])

def py25hash(self):
 if not self:
 return 0 # empty
 value = ord(self[0]) &lt;&lt; 7
 for char in self:
 value = c_mul(1000003, value) ^ ord(char)
 value = value ^ len(self)
 if value == -1:
 value = -2
 if value &gt;= 2**63:
 value -= 2**64
 return value
</code></pre>

blocks|key|1573831|text|字符串的多项式哈希。1000000009和239是任意质数。不太可能意外地发生碰撞。模运算不是很快，但为了防止冲突，这比对2取模更可靠。当然，故意发现冲突是很容易的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1573832|mod=1000000009
def+hash(s):
++++result=0
++++for+c+in+s:
++++++++result+=+(result+*+239+%2B+ord(c))+%25+mod
++++return+result+%25+mod|code-block|syntax|javascript|1573833|entityMap^0|A|A|L|3|1P|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Polynomial hash for strings. <code>1000000009</code> and <code>239</code> are arbitrary prime numbers. Unlikely to have collisions by accident. Modular arithmetic is not very fast, but for preventing collisions this is more reliable than taking it modulo a power of <code>2</code>. Of course, it is easy to find a collision on purpose.

<pre><code>mod=1000000009
def hash(s):
 result=0
 for c in s:
 result = (result * 239 + ord(c)) % mod
 return result % mod
</code></pre>

blocks|key|1358579|text|PYTHONHASHSEED的值可用于初始化散列值。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1358580|尝试：|1358581|PYTHONHASHSEED+python+-c+'print(hash('http://stackoverflow.com'))'|code-block|syntax|javascript|1358582|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/using/cmdline.html#envvar-PYTHONHASHSEED^0|0|E|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

The value of <a href="https://docs.python.org/3/using/cmdline.html#envvar-PYTHONHASHSEED" rel="nofollow">PYTHONHASHSEED</a> might be used to initialize the hash values.

Try:

<pre><code>PYTHONHASHSEED python -c 'print(hash('http://stackoverflow.com'))'
</code></pre>

Windows XP, Python 2.5:

<pre><code>hash('http://stackoverflow.com') Result: 1934711907
</code></pre>

Google App Engine (<a href="http://shell.appspot.com/" rel="nofollow noreferrer">http://shell.appspot.com/</a>):

<pre><code>hash('http://stackoverflow.com') Result: -5768830964305142685
</code></pre>

Why is that? How can I have a hash function that will give me same results across different platforms (Windows, Linux, Mac)?

Built in Python hash() function

Windows

Python

Linux

Windows XP、Python 2.5：hash('http://stackoverflow.com') Result: 1934711907谷歌应用引擎()：hash('http://stackoverflow.com') Result: -5768830964305142685为什么会这样呢？如何使用散列函数在...

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