Does Python do slice-by-reference on strings?

开发者_JAVA百科I want to know if when I do something like

a = "This could be a very large string..."
b = a[:10]

a new string is created or a view/iterator is returned

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Python does slice-by-copy, meaning every time you slice (except for very trivial slices, such as a[:]), it copies all of the data into a new string object.

According to one of the developers, this choice was made because

The [slice-by-reference] approach is more complicated, harder to implement and may lead to unexpected behavior.

For example:

a = "a long string with 500,000 chars ..."
b = a[0]
del a

With the slice-as-copy design the string a is immediately freed. The slice-as-reference design would keep the 500kB string in memory although you are only interested in the first character.

Apparently, if you absolutely need a view into a string, you can use a memoryview object.

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When you slice strings, they return a new instance of String. Strings are immutable objects.