Reputation: 1500
Looking at the following IPython (Python 3.7) session:
In [1]: id('hello')
Out[1]: 140300950123104
In [2]: id('hello')
Out[2]: 140300963300384
In [3]: 'hello' is 'hello'
Out[3]: True
In [4]: '{} - {}'.format(id('hello'), id('hello'))
Out[4]: '140300946565808 - 140300946565808'
Expressions 1 and 2 indicate that each time the string hello
is initialized, it does get a different id. However, when initialized in the same expression, they seem to get the same id as the results of expressions 3 and 4 suggest. Why is that so?
Upvotes: 3
Views: 1072
Reputation: 37327
This is an interesting question, but it's well explained in wtfpython.
When a and b are set to "hello" in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already
hello
as an object(because "hello" is not implicitly interned as per the facts mentioned above). It's a compiler optimization and specifically applies to the interactive environment.
One thing that differs is that in IPython, things might be a bit different from direct Python REPL, so this explains the difference in id
in your first two inputs.
Upvotes: 3
Reputation: 19
Two objects with non-overlapping lifetimes may have the same id() value.
Upvotes: 0