This has to do with how is works. It checks for references instead of value. It returns True if either argument is assigned to the same object. In this case, they are different instances; float(0) and float(0) have the same value ==, but are distinct entities as far as Python is concerned. CPython implementation also … Read more
Yes, that’s a good approximation of how the for loop construct is implemented. It certainly matches the for loop statement documentation: The expression list is evaluated once; it should yield an iterable object. An iterator is created for the result of the expression_list. The suite is then executed once for each item provided by the … Read more
They are not randomly ordered, they are arbitrarily ordered. It means you should not count on the order of insertions being maintained as the actual internal implementation details determine the order instead. The order depends on the insertion and deletion history of the set. In CPython, sets use a hash table, where inserted values are … Read more
Well you have a total of 4 questions, let us go one by one. 1. Why does str(list) returns how we see list on the console? How does str(list) work? What is str() and __str__()? The str() callable is to return a printable form of the object only! From the docs str(object) does not always … 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
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 problem being solved is that the previous hash algorithm in Lib/sets.py had horrendous performance on datasets that arise in a number of graph algorithms (where nodes are represented as frozensets): # Old-algorithm with bad performance def _compute_hash(self): result = 0 for elt in self: result ^= hash(elt) return result def __hash__(self): if self._hashcode is … Read more
With a list literal, the VM creates the list with a set length. When passing a sequence to the list() constructor the elements are added one by one (via list.extend()) and as such the list is resized when appropriate. Since the resize operation overallocates in order to amortize the cost, the final list will usually … Read more
If I know the number of keys and exactly what are those keys, is there any way in python to make a dict (or a hashtable) work more efficiently? I vaguely remember that if you know the keys, you can design the hash function smartly (perfect hash?) and allocate the space beforehand. Python doesn’t expose … Read more
These attributes are there to enable introspection for Python objects defined in C code. The C-API Argument Clinic provides the data, to assist the inspect module when building Signature objects. Introspection of C-API functions was not supported before. See the internal inspect._signature_fromstr() function on how the __text_signature__ value is used. Currently, the __text_signature__ attribute is … Read more