if else in a list comprehension
Do-something if <condition>, else do-something else.
Open a URL in a new tab (and not a new window)
Nothing an author can do can choose to open in a new tab instead of a new window; it is a user preference. (Note that the default user preference in most browsers is for new tabs, so a trivial test on a browser where that preference hasn’t been changed will not demonstrate this.) CSS3 proposed target-new, but the … Read more
How do I get into a Docker container’s shell?
docker attach will let you connect to your Docker container, but this isn’t really the same thing as ssh. If your container is running a webserver, for example, docker attach will probably connect you to the stdout of the web server process. It won’t necessarily give you a shell. The docker exec command is probably what you are looking for; this will let … Read more
What’s the difference between ISO 8601 and RFC 3339 Date Formats?
Is one just an extension? Pretty much, yes – RFC 3339 is listed as a profile of ISO 8601. Most notably RFC 3339 specifies a complete representation of date and time (only fractional seconds are optional). The RFC also has some small, subtle differences. For example truncated representations of years with only two digits are not allowed … Read more
Remove element by id
The DOM is organized in a tree of nodes, where each node has a value, along with a list of references to its child nodes. So element.parentNode.removeChild(element) mimics exactly what is happening internally: First you go the parent node, then remove the reference to the child node. As of DOM4, a helper function is provided to do … Read more
Why is the time complexity of both DFS and BFS O( V + E )
Your sum can be rewritten as and the first group is O(N) while the other is O(E).
No space left on device
Such difference between the output of du -sh and df -h may happen if some large file has been deleted, but is still opened by some process. Check with the command lsof | grep deleted to see which processes have opened descriptors to deleted files. You can restart the process and the space will be freed.
if A vs if A is not None:
The statement will call A.__nonzero__() (see Special method names documentation) and use the return value of that function. Here’s the summary: object.__nonzero__(self) Called to implement truth value testing and the built-in operation bool(); should return False or True, or their integer equivalents 0 or 1. When this method is not defined, __len__() is called, if it is defined, and the object is considered true if its result is … Read more
How can I revert multiple Git commits (already pushed) to a published repository?
The Problem There are a number of work-flows you can use. The main point is not to break history in a published branch unless you’ve communicated with everyone who might consume the branch and are willing to do surgery on everyone’s clones. It’s best not to do that if you can avoid it. Solutions for … Read more