python - sys.intern() 无法在切片时实习字符串

Question

为什么 sys.intern() 无法实习该字符串？

>>> from sys import intern
>>> "abcd"[:-1] == "abc"
True
>>> "abcd"[:-1] is "abc"
False
>>> intern("abc")
'abc'
>>> "abcd"[:-1] is "abc"
False  # Expected True

(在 CPython 3.7.4 上)

Answer 1

字符串文字已经被保留，它是您需要手动保留的计算表达式。

from sys import intern
print("abcd"[:-1] is "abc")  # False
print(intern("abcd"[:-1]) is "abc")  # True
print("abcd"[:-1] is "abc")  # False

intern 并不意味着“每当程序中的任何位置生成此字符串时，都将其更改为驻留引用”，它只是返回给定字符串的驻留引用。

s1 = "abc"
s2 = "abc"
s3 = "abcd"[:-1]
s4 = intern(s3)
for s in [s1, s2, s3, s4]:
  print(id(s))

140002991598512
140002991598512
140002990838576
140002991598512