The del statement doesn’t reclaim memory. It removes a reference, which decrements the reference count on the value. If the count is zero, the memory can be reclaimed. CPython will reclaim the memory immediately, there’s no need to wait for the garbage collector to run. In fact, the garbage collector is only needed for reclaiming … Read more
A package is only read from disk once and then stored in memory as mutable singleton. The second time you import it you get the exact same singleton you have previously imported, and it’s still missing its cos. del math merely deletes the local name for it, it doesn’t “unimport” the package from Python overall.
tl;dr; mylist.clear() # Added in Python 3.3 del mylist[:] are probably the best ways to do this. The rest of this answer tries to explain why some of your other efforts didn’t work. cpython at least works on reference counting to determine when objects will be deleted. Here you have multiple references to the same … Read more
You cannot assume that __del__ will ever be called – it is not a place to hope that resources are automagically deallocated. If you want to make sure that a (non-memory) resource is released, you should make a release() or similar method and then call that explicitly (or use it in a context manager as … Read more
The first is more efficient than the second. del foo.bar compiles to two bytecode instructions: 2 0 LOAD_FAST 0 (foo) 3 DELETE_ATTR 0 (bar) whereas delattr(foo, “bar”) takes five: 2 0 LOAD_GLOBAL 0 (delattr) 3 LOAD_FAST 0 (foo) 6 LOAD_CONST 1 (‘bar’) 9 CALL_FUNCTION 2 12 POP_TOP This translates into the first running slightly faster … Read more
Firstly, you can del other things besides local variables del list_item[4] del dictionary[“alpha”] Both of which should be clearly useful. Secondly, using del on a local variable makes the intent clearer. Compare: del foo to foo = None I know in the case of del foo that the intent is to remove the variable from … Read more
The del statement removes an element: del d[key] Note that this mutates the existing dictionary, so the contents of the dictionary changes for anybody else who has a reference to the same instance. To return a new dictionary, make a copy of the dictionary: def removekey(d, key): r = dict(d) del r[key] return r The … Read more