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pythondata-structuresaliasnamingmutable

Alias for long list name and modification

I have a nested data structure (e.g. mydict[names[num]]) which is difficult to read in code. Hence I would like to create a proxy (alias) and use it to modify this structure.

long_name = [1,2,3]
short = long_name
assert id(long_name) == id(short)

short.append(4)
assert id(long_name) == id(short)

short = [n**2 for n in short]
assert id(long_name) == id(short)  # AssertionError

Given the AssertionError on id(a) = id(b), do I understand correctly python separates short and long_name during comprehension and allocates separate memory?

In practice, my structure contains millions of long strings, so takes up a lot of space (memory), hence this concern.

Solution

  • When long_name and short are associated with the same object, you can call its methods as many times as you like and both variables will not change, but comprehension will create a new object and you will link your short variable to it. Now you have 2 variables associated with 2 different objects and 2 different links.