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How can I create a copy of an object in Python?
...tainer.
list.copy is a shallow copy:
>>> list_of_dict_of_set = [{'foo': set('abc')}]
>>> lodos_copy = list_of_dict_of_set.copy()
>>> lodos_copy[0]['foo'].pop()
'c'
>>> lodos_copy
[{'foo': {'b', 'a'}}]
>>> list_of_dict_of_set
[{'foo': {'b', 'a'}}]
You don...
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 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...
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...
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...
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 ...