Why is this interface used? Because it supports the basic operations that would allow a client programmer to iterate over any kind of collection (note: not necessarily a Collection in the Object sense). Why are the methods… not directly coded to the data structure implementation itself? They are, they’re just marked Private so you can’t … Read more
Why? Because if you force iterator to have a reset method every iterator has to have a reset method. That gives every iterator writer extra work. Plus some iterators are really hard (or really expensive) to reset, and you wouldn’t want users to call reset on them. Iterators over files or streams are good examples. … Read more
name_map = {‘oldcol1’: ‘newcol1’, ‘oldcol2’: ‘newcol2’, ‘oldcol3’: ‘newcol3’…} for row in rows: # Each row is a dict of the form: {‘oldcol1’: ‘…’, ‘oldcol2’: ‘…’} row = dict((name_map[name], val) for name, val in row.iteritems()) … Or in Python2.7+ with Dict Comprehensions: for row in rows: row = {name_map[name]: val for name, val in row.items()}
In C++ an Iterator is a concept, not a concrete (or abstract) type, but any type that obeys certain iterator like rules. For example iterators generally can be incremented ++i. They can be accessed (dereferenced) *i to obtain the value they currently point to. They are essentially abstractions of a pointer. In the Standard Library’s … Read more
Surprisingly, C++98 and C++11 didn’t say that you can compare a iterator with a const_iterator. This leads to LWG issue 179 and LWG issue 2263. Now in C++14, this is explicitly permitted by ยง 23.2.1[container.requirements.general]p7 In the expressions i == j i != j i < j i <= j i >= j i > … Read more
JavaScript has a foreach-style loop (for (x in a)), but it is extremely bad coding practice to use it on an Array. Basically, the array.length approach is correct. There is also a a.forEach(fn) method in newer JavaScripts you can use, but it is not guaranteed to be present in all browsers – and it’s slower … Read more
C++ copy/move ctor/assign are safe for regular value types. Regular value types behave like integers or other “regular” values. They are also safe for pointer semantic types, so long as the operation does not change what the pointer “should” point to. Pointing to something “within yourself”, or another member, is an example of where it … Read more
To address the two examples you brought up: import itertools data1 = range(10) # This creates a NEW list data1[2:5] # This creates an iterator that iterates over the EXISTING list itertools.islice(data1, 2, 5) data2 = [1, 2, 3] data3 = [4, 5, 6] # This creates a NEW list data2 + data3 # This … Read more
I don’t know if this was the original error but you can get the same error if you try to call f.tell() inside of a line-by-line iteration of a file like so: with open(path, “r+”) as f: for line in f: f.tell() #OSError which can be easily substituted by the following: with open(path, mode) as … Read more
This will work with any random-access iterator, such as one from vector or deque: std::vector<int>::iterator iter = v.begin() + 10; If you want a solution that will work for any type of iterator, use next: std::vector<int>::iterator iter = std::next(v.begin(), 10); Or if you’re not on a C++11 implementation, advance: std::vector<int>::iterator iter = v.begin(); std::advance(iter, 10);