The time complexity is O(N) on average, O(NM) worst case (N being the length of the longer string, M, the shorter string you search for). As of Python 3.10, heuristics are used to lower the worst-case scenario to O(N + M) by switching algorithms. The same algorithm is used for str.index(), str.find(), str.__contains__() (the in … Read more
The main logic of creating a function is to isolate the comprehension’s iteration variablepeps.python.org. By creating a function: Comprehension iteration variables remain isolated and don’t overwrite a variable of the same name in the outer scope, nor are they visible after the comprehension However, this is inefficient at runtime. Due to this reason, python-3.12 implemented … Read more
I checked the source code of the bytecode (python 3.11.6) and found that in the decompiled bytecode, it seems that only JUMP_BACKWARD will execute a warmup function, which will trigger specialization in python 3.11 when executed enough times: PyObject* _Py_HOT_FUNCTION _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag) { /* … */ TARGET(JUMP_BACKWARD) { _PyCode_Warmup(frame->f_code); JUMP_TO_INSTRUCTION(JUMP_BACKWARD_QUICK); } … Read more
You should watch this video (although it is CPython1 specific and about dictionaries — but I assume it applies to sets as well). Basically, python hashes the elements and takes the last N bits (where N is determined by the size of the set) and uses those bits as array indices to place the object … Read more
What Happened? When you use next(iter(instance_of_Class2)), iter() calls .close() on the inner generator when it (the iterator, not the generator!) goes out of scope (and is deleted), while with Class1, iter() only closes its instance >>> g = (i for i in range(3)) >>> b = Class2(g) >>> i = iter(b) # hold iterator open … Read more
There are two different characters involved here. One is the MICRO SIGN, which is the one on the keyboard, and the other is GREEK SMALL LETTER MU. To understand what’s going on, we should take a look at how Python defines identifiers in the language reference: identifier ::= xid_start xid_continue* id_start ::= <all characters in … Read more
For an OrderedDict it’s inherently O(n) because the ordering is recorded in a linked list. For the builtin dict, there’s a vector (a contiguous array) rather than a linked list, but pretty much the same thing in the end: the vector contains a few kind of “dummies”, special internal values that mean “no key has … Read more
A function call requires that the current execution frame is suspended, and a new frame is created and pushed on the stack. This is relatively expensive, compared to many other operations. You can measure the exact time required with the timeit module: >>> import timeit >>> def f(): pass … >>> timeit.timeit(f) 0.15175890922546387 That’s 1/6th … Read more
It is set to the absolute name of the module as imported. If you imported it as foo.bar, then __name__ is set to ‘foo.bar’. The name is determined in the import.c module, but because that module handles various different types of imports (including zip imports, bytecode-only imports and extension modules) there are several code paths … Read more
The entire reason lambda exists is that it’s an expression.1 If you want something that’s like lambda but is a statement, that’s just def. Python expressions cannot contain statements. This is, in fact, fundamental to the language, and Python gets a lot of mileage out of that decision. It’s the reason indentation for flow control … Read more