时间:2020-07-07 python教程 查看: 959
前言
在 Python 中经常通过内存池化技术来提高其性能,那么问题来了,在什么情况下会池化呢? 让我们通过几个例子进行一下理解一下.
预备知识
在查看例子之前,首先要提 python 中的一个函数 id(),让我们看一下函数说明:
id(obj, /)
Return the identity of an object.
This is guaranteed to be unique among simultaneously existing objects.
(CPython uses the object \'s memory address.)
通过上述说明,可以得知 id() 将会返回对像的唯一标识,在 CPython 中将会返回内存地址,也就是说如果两个对象 的 id 值一样,可以说着两个对象是相同的了.
例子
example 00
a = ""
b = ""
print(id(a),id(b))
print(a is b)
输出结果:
>>> a = ""
>>> b = ""
>>> print(id(a),id(b))
2114853370544 2114853370544
>>> print(a is b)
True
example 01
a = "a"
b = "a"
print(id(a),id(b))
print(a is b)
输出结果:
>>> a = "a"
>>> b = "a"
>>> print(id(a),id(b))
2114883022608 2114883022608
>>> print(a is b)
True
example 02
a = "magic_string"
b = "magic" + "_" + "string"
print(id(a),id(b))
print(a is b)
输出结果:
>>> a = "magic_string"
>>> b = "magic" + "_" + "string"
>>> print(id(a),id(b))
2114887161136 2114887161136
>>> print(a is b)
True
example 03
a = "magic!"
b = "mgaic!"
print(id(a),id(b))
print(a is b)
输出结果:
>>> a = "magic!"
>>> b = "mgaic!"
>>> print(id(a),id(b))
2114885855416 2114889455408
>>> print(a is b)
False
example 04
a,b = "magic!","magic!"
print(id(a),id(b))
print(a is b)
输出结果:
>>> a,b = "magic!","magic!"
>>> print(id(a),id(b))
2114885691912 2114885691912
>>> print(a is b)
True
example 05
a = "!"
b = "!"
print(id(a),id(b))
print(a is b)
输出结果:
>>> a = "!"
>>> b = "!"
>>> print(id(a),id(b))
140564571922024 140564571922024
>>> print(a is b)
True
example 06
print(a*20 is 'aaaaaaaaaaaaaaaaaaaa')
print(a*21 is 'aaaaaaaaaaaaaaaaaaaaa')
输出结果:
>>> print(a*20 is 'aaaaaaaaaaaaaaaaaaaa')
False
>>> print(a*21 is 'aaaaaaaaaaaaaaaaaaaaa')
False
总结
通过上述 7 个例子,我们不难对 python 的字符串池化有个大概的认识,我们这里做个简单的总结:
参考链接
The internals of Python string interning
Python String objects implementation
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