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What is the best way to implement nested dictionaries?
...getting this behavior, here's how to shoot yourself in the foot:
Implement __missing__ on a dict subclass to set and return a new instance.
This approach has been available (and documented) since Python 2.5, and (particularly valuable to me) it pretty prints just like a normal dict, instead of the u...
Override Python's 'in' operator?
...
MyClass.__contains__(self, item)
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How can I filter a date of a DateTimeField in Django?
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Such lookups are implemented in django.views.generic.date_based as follows:
{'date_time_field__range': (datetime.datetime.combine(date, datetime.time.min),
datetime.datetime.combine(date, datetime.time.max))}
Because it is quite verbose there are pla...
How do I list all files of a directory?
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A bit simpler: (_, _, filenames) = walk(mypath).next() (if you are confident that the walk will return at least one value, which it should.)
– misterbee
Jul 14 '13 at 20:56
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Remove all occurrences of a value from a list?
...ython 3.x
>>> x = [1,2,3,2,2,2,3,4]
>>> list(filter((2).__ne__, x))
[1, 3, 3, 4]
or
>>> x = [1,2,3,2,2,2,3,4]
>>> list(filter(lambda a: a != 2, x))
[1, 3, 3, 4]
Python 2.x
>>> x = [1,2,3,2,2,2,3,4]
>>> filter(lambda a: a != 2, x)
[1, 3, 3...
What does $_ mean in PowerShell?
...ich is called $PSItem in Powershell 3 and newer.
1,2,3 | %{ write-host $_ }
or
1,2,3 | %{ write-host $PSItem }
For example in the above code the %{} block is called for every value in the array. The $_ or $PSItem variable will contain the current value.
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namedtuple and default values for optional keyword arguments
...Node()
Node(val=None, left=None, right=None)
Before Python 3.7
Set Node.__new__.__defaults__ to the default values.
>>> from collections import namedtuple
>>> Node = namedtuple('Node', 'val left right')
>>> Node.__new__.__defaults__ = (None,) * len(Node._fields)
>&g...
Where should signal handlers live in a django project?
...ke:
yourapp/signals/handlers.py:
from django.db.models.signals import pre_save
from django.dispatch import receiver
from myapp.models import MyModel
@receiver(pre_save, sender=MyModel)
def my_handler(sender, **kwargs):
pass
The best place to register your signal handler is then in the AppCo...
Mongoose, Select a specific field with find
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The _id field is always present unless you explicitly exclude it. Do so using the - syntax:
exports.someValue = function(req, res, next) {
//query with mongoose
var query = dbSchemas.SomeValue.find({}).select('name -_id'...
Why would you use an ivar?
...d by the compiler may involve another C function call to the functions objc_getProperty/objc_setProperty, as these will have to retain/copy/autorelease the objects as needed and further perform spinlocking for atomic properties where necessary. This can easily get very expensive and I'm not talking ...