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What does the “yield” keyword do?
... list, you can read its items one by one. Reading its items one by one is called iteration:
>>> mylist = [1, 2, 3]
>>> for i in mylist:
... print(i)
1
2
3
mylist is an iterable. When you use a list comprehension, you create a list, and so an iterable:
>>> mylist = [...
Difference between Python's Generators and Iterators
...ry generator is an iterator, but not vice versa. A generator is built by calling a function that has one or more yield expressions (yield statements, in Python 2.5 and earlier), and is an object that meets the previous paragraph's definition of an iterator.
You may want to use a custom iterator, ra...
Creating a singleton in Python
...mple implementation:
class Singleton(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
return cls._instances[cls]
class Logger(object):
__meta...
What is the id( ) function used for?
... Python objects.
Is it the same with memory addresses in C?
Conceptually, yes, in that they are both guaranteed to be unique in their universe during their lifetime. And in one particular implementation of Python, it actually is the memory address of the corresponding C object.
If yes, wh...
How to combine two or more querysets in a Django view?
...sets into a list is the simplest approach. If the database will be hit for all querysets anyway (e.g. because the result needs to be sorted), this won't add further cost.
from itertools import chain
result_list = list(chain(page_list, article_list, post_list))
Using itertools.chain is faster than...
How does JavaScript .prototype work?
...ing languages but I've written my fair share of JavaScript code. I never really got my head around this prototype-based programming, does any one know how this works?
...
How to import other Python files?
...
importlib was added to Python 3 to programmatically import a module.
It is just a wrapper around __import__, see the docs.
import importlib
moduleName = input('Enter module name:')
importlib.import_module(moduleName)
Note: the .py extension should be removed from mod...
Accessing dict keys like an attribute?
...__init__(*args, **kwargs)
self.__dict__ = self
Some pros:
It actually works!
No dictionary class methods are shadowed (e.g. .keys() work just fine. Unless - of course - you assign some value to them, see below)
Attributes and items are always in sync
Trying to access non-existent key as an...
What's the best way to send a signal to all members of a process group?
... And if you modify the format slightly and sort, you get to see all processes nicely grouped and beginning with (potentially) the group parent in each group: ps x -o "%r %p %y %x %c" | sort -nk1,2
– haridsv
Dec 3 '12 at 12:18
...
How to implement “select all” check box in HTML?
.../script>
<input type="checkbox" onClick="toggle(this)" /> Toggle All<br/>
<input type="checkbox" name="foo" value="bar1"> Bar 1<br/>
<input type="checkbox" name="foo" value="bar2"> Bar 2<br/>
<input type="checkbox" name="foo" value="bar3"> Bar 3<br/&...