大约有 12,000 项符合查询结果（耗时：0.0316秒） [XML]
What is the meaning of single and double underscore before an object name?
...single leading underscore isn't exactly just a convention: if you use from foobar import *, and module foobar does not define an __all__ list, the names imported from the module do not include those with a leading underscore. Let's say it's mostly a convention, since this case is a pretty obscure co...
What does the exclamation mark mean in a Haskell declaration?
.... Let's look at an example, so that we can see just what this means:
data Foo = Foo Int Int !Int !(Maybe Int)
f = Foo (2+2) (3+3) (4+4) (Just (5+5))
The function f above, when evaluated, will return a "thunk": that is, the code to execute to figure out its value. At that point, a Foo doesn't eve...
How do I parse command line arguments in Bash?
...cluded a simplistic getopts example.
Usage demo-getopts.sh -vf /etc/hosts foo bar
cat >/tmp/demo-getopts.sh <<'EOF'
#!/bin/sh
# A POSIX variable
OPTIND=1 # Reset in case getopts has been used previously in the shell.
# Initialize our own variables:
output_file=""
verbose=0
whil...
Hidden features of Python [closed]
...
Creating generators objects
If you write
x=(n for n in foo if bar(n))
you can get out the generator and assign it to x. Now it means you can do
for n in x:
The advantage of this is that you don't need intermediate storage, which you would need if you did
x = [n for n in foo...
What is the (function() { } )() construct in JavaScript?
...e it’s often used as this:
(function(){
// all your code here
var foo = function() {};
window.onload = foo;
// ...
})();
// foo is unreachable here (it’s undefined)
Correction suggested by Guffa:
The function is executed right after it's created, not after it is parsed. The enti...
Returning value from Thread
...
Usually you would do it something like this
public class Foo implements Runnable {
private volatile int value;
@Override
public void run() {
value = 2;
}
public int getValue() {
return value;
}
}
Then you can create the thread and...
Primary key or Unique index?
...lues in that column in two different rows. Example:
CREATE TABLE table1 (foo int, bar int);
CREATE UNIQUE INDEX ux_table1_foo ON table1(foo); -- Create unique index on foo.
INSERT INTO table1 (foo, bar) VALUES (1, 2); -- OK
INSERT INTO table1 (foo, bar) VALUES (2, 2); -- OK
INSERT INTO table1 (f...
Does python have an equivalent to Java Class.forName()?
... only refer to the top level module,
For example, if your class lives in foo.baz module, then m will be the module foo
We can easily obtain a reference to foo.baz using getattr( m, 'baz' )
To get from the top level module to the class, have to recursively use gettatr on the parts of the class nam...
Passing variables in remote ssh command
...ariables.
# The first one even contains whitespace and a newline.
readonly FOO=$'apjlljs ailsi \n ajlls\t éjij'
readonly BAR=ygnàgyààynygbjrbjrb
# Make a list of what you want to pass through SSH.
# (The “unset” is just in case someone exported
# an associative array with this name.)
unset ...
Dynamic constant assignment
...ject itself is different each time the method is called. For example:
def foo
p "bar".object_id
end
foo #=> 15779172
foo #=> 15779112
Perhaps if you explained your use case—why you want to change the value of a constant in a method—we could help you with a better implementation.
Per...