问题
This question already has an answer here:
- About the changing id of an immutable string 5 answers
>>> s1 = \"spam\"
>>> s2 = \"spam\"
>>> s1 is s2
True
>>> q = \'asdalksdjfla;ksdjf;laksdjfals;kdfjasl;fjasdf\'
>>> r = \'asdalksdjfla;ksdjf;laksdjfals;kdfjasl;fjasdf\'
>>> q is r
False
How many characters should have to s1 is s2 give False? Where is limit? I.e., I am asking how long a string has to be before python starts making separate copies of it.
回答1:
String interning is implementation specific and shouldn't be relied upon, use equality testing if you want to check two strings are identical.
回答2:
If you want, for some bizarre reason, to force the comparison to be true then use the intern function:
>>> a = intern('12345678012345678901234567890qazwsxedcrfvtgbyhnujmikolp')
>>> b = intern('12345678012345678901234567890qazwsxedcrfvtgbyhnujmikolp')
>>> a is b
True
回答3:
Here is a piece of comment about interned string from CPython 2.5.0 source file (stringobject.h)
/* ... ... This is generally restricted to strings that **"look like" Python identifiers**, although the intern() builtin can be used to force interning of any string ... ... */
Accordingly, strings contain only underscores, digits or alphabets will be interned. In your example, q and ``r contain ;, so they will not be interned.
来源：https://stackoverflow.com/questions/10622472/when-does-python-choose-to-intern-a-string