Strange behaviour related to apparent caching of "{}"
python
Solution
It's not being cached -- if you don't assign the result of `{}` anywhere, its reference count is 0 and it's cleaned up right away. It just happened that the next one you allocated reused the memory from the old one. When you assign it to `x` you keep it alive, and then the next one has a different address.
In your function example, once `f` returns there are no remaining references to your dict, so it gets cleaned up too, and the same thing applies.
Problem
Today I learned that Python caches the expression `{}`, and replaces it with a new empty dict when it's assigned to a variable: ``` print id({}) # 40357936 print id({}) # 40357936 x = {} print id(x) # 40357936 print id({}) # 40356432 ``` I haven't looked at the source code, but I have an idea as to how this might be implemented. (Maybe when the reference count to the global `{}` is incremented, the global `{}` gets replaced.) But consider this bit: ``` def f(x): x['a'] = 1 print(id(x), x) print(id(x)) # 34076544 f({}) # (34076544, {'a': 1}) print(id({}), {}) # (34076544, {}) print(id({})) # 34076544 ``` `f` modifies the global dict without causing it to be replaced, and it prints out the modified dict. But outside of `f`, despite the id being the same, the global dict is now empty! What is happening??