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Difference between single and double square brackets in Bash
...nt of [ that prevents further arguments from being used.
Ubuntu 16.04 actually has an executable for it at /usr/bin/[ provided by coreutils, but the bash built-in version takes precedence.
Nothing is altered in the way that Bash parses the command.
In particular, < is redirection, && a...
When to use generic methods and when to use wild-card?
...eed such kind of relation, then you are free not to use type parameters at all.
Some other difference between using wildcards and type parameters are:
If you have only one parameterized type argument, then you can use wildcard, although type parameter will also work.
Type parameters support multi...
Omitting the second expression when using the if-else shorthand
...o an option:
x==2 && dosomething();
dosomething() will only be called if x==2 is evaluated to true. This is called Short-circuiting.
It is not commonly used in cases like this and you really shouldn't write code like this. I encourage this simpler approach:
if(x==2) dosomething();
You...
In Python, when to use a Dictionary, List or Set?
...tion of unique elements, use a set. (For example, when you want the set of all the words used in a document).
When you want to collect an immutable ordered list of elements, use a tuple. (For example, when you want a (name, phone_number) pair that you wish to use as an element in a set, you would n...
When should I use the Visitor Design Pattern? [closed]
...want to make the fewest possible modifications to it.
The Visitor pattern allows you to move each new operation in a suitable class, and you need to extend the hierarchy's interface only once. Let's do it. First, we define an abstract operation (the "Visitor" class in GoF) which has a method for ev...
Why do I need 'b' to encode a string with Base64?
...-z, 0-9, +, /* so it can be transmitted over channels that do not preserve all 8-bits of data, such as email.
Hence, it wants a string of 8-bit bytes. You create those in Python 3 with the b'' syntax.
If you remove the b, it becomes a string. A string is a sequence of Unicode characters. base64 ha...
How to sort a list of strings?
What is the best way of creating an alphabetically sorted list in Python?
11 Answers
1...
INSERT INTO…SELECT for all MySQL columns
... syntax, it looks like this (leave out the column list to implicitly mean "all")
INSERT INTO this_table_archive
SELECT *
FROM this_table
WHERE entry_date < '2011-01-01 00:00:00'
For avoiding primary key errors if you already have data in the archive table
INSERT INTO this_table_archive
SELECT...
Django TemplateDoesNotExist?
... assuming that you have the apps configured in settings.py like this:
INSTALLED_APPS = (
'appname1',
'appname2',
'appname3',
)
By default Django will load the templates under templates/ directory under every installed apps. So with your directory structure, we want to move our templat...
What is your preferred style for naming variables in R? [closed]
...
Good previous answers so just a little to add here:
underscores are really annoying for ESS users; given that ESS is pretty widely used you won't see many underscores in code authored by ESS users (and that set includes a bunch of R Core as well as CRAN authors, excptions like Hadley notwithsta...