Is there a more elegant way for unpacking keys and values of a dictionary into two lists, without losing consistence?
keys, values = zip(*d.items())
iterable-unpacking
Why is it valid to assign to an empty list but not to an empty tuple?
The comment by @user2357112 that this seems to be coincidence appears to be correct. The relevant part of the Python source code is in Python/ast.c: switch (e->kind) { # several cases snipped case List_kind: e->v.List.ctx = ctx; s = e->v.List.elts; break; case Tuple_kind: if (asdl_seq_LEN(e->v.Tuple.elts)) { e->v.Tuple.ctx = ctx; s = e->v.Tuple.elts; } else { … Read more
Python: Splat/unpack operator * in python cannot be used in an expression?
Unpacking in list, dict, set, and tuple literals has been added in Python 3.5, as described in PEP 448: Python 3.5.0 (v3.5.0:374f501f4567, Sep 13 2015, 02:27:37) on Windows (64 bits). >>> [1, 2, 3, *[4, 5, 6]] [1, 2, 3, 4, 5, 6] Here are some explanations for the rationale behind this change. Note that … Read more
Python star unpacking for version 2.7
in python 2.X, you can do: c = (1, 2, 3) a, b = c[0], c[1:] as long as c has at least one member it will work because if c only has 1 thing in it c[1:] is []. You should probably make sure there is at least one thing in c though, or … Read more
Python update object from dictionary
there is also another way of doing it by looping through the items in d. this doesn’t have the same assuption that they will get stored in c.__dict__ which isn’t always true. d = {‘bar’: 456} for key,value in d.items(): setattr(c,key,value) or you could write a update method as part of MyClass so that c.update(d) … Read more
Is it possible to unpack a tuple in Python without creating unwanted variables?
In Python the _ is often used as an ignored placeholder. (path, _) = self._treeView.get_cursor() You could also avoid unpacking as a tuple is indexable. def get_selected_index(self): return self._treeView.get_cursor()[0][0]
How do I convert a tuple of tuples to a one-dimensional list using list comprehension? [duplicate]
it’s typically referred to as flattening a nested structure. >>> tupleOfTuples = ((1, 2), (3, 4), (5,)) >>> [element for tupl in tupleOfTuples for element in tupl] [1, 2, 3, 4, 5] Just to demonstrate efficiency: >>> import timeit >>> it = lambda: list(chain(*tupleOfTuples)) >>> timeit.timeit(it) 2.1475738355700913 >>> lc = lambda: [element for tupl in … Read more
How does swapping of members in tuples (a,b)=(b,a) work internally?
Python separates the right-hand side expression from the left-hand side assignment. First the right-hand side is evaluated, and the result is stored on the stack, and then the left-hand side names are assigned using opcodes that take values from the stack again. For tuple assignments with 2 or 3 items, Python just uses the stack … Read more
Unpacking generalizations
Taking a quote from the Py-Dev mailing list thread in which this feature was accepted: So that leaves comprehensions. IIRC, during the development of the patch we realized that f(*x for x in xs) is sufficiently ambiguous that we decided to disallow it — note that f(x for x in xs) is already somewhat of … Read more