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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...
SqlAlchemy - Filtering by Relationship Attribute
...ts = Patient.query.filter(Patient.mother.has(phenoscore=10))
or join (usually faster):
patients = Patient.query.join(Patient.mother, aliased=True)\
.filter_by(phenoscore=10)
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Checking whether a variable is an integer or not [duplicate]
...t use type. It is almost never the right answer in Python, since it blocks all the flexibility of polymorphism. For instance, if you subclass int, your new class should register as an int, which type will not do:
class Spam(int): pass
x = Spam(0)
type(x) == int # False
isinstance(x, int) # True
Thi...
Unix's 'ls' sort by name
...t the FILEs (the current directory by default). Sort entries alpha‐betically if none of -cftuvSUX nor --sort is specified.:
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Use StringFormat to add a string to a WPF XAML binding
... number and units isn't fixed. <Run Text="{x:Static s:UIStrings.General_FahrenheitAbbreviation}" />
– Matt Becker
Nov 10 '15 at 15:19
...
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...
“var” or no “var” in JavaScript's “for-in” loop?
...erties, so using the standard "for in" loop w/o the var statement will actually fail and return a ReferenceError.
– dkugappi
Jun 11 '13 at 15:01
2
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Generate a random point within a circle (uniformly)
...triangle ABC, where |AB|=|BC|? Let's make this easier by extending to a parallelogram ABCD. It's easy to generate points uniformly in ABCD. We uniformly pick a random point X on AB and Y on BC and choose Z such that XBYZ is a parallelogram. To get a uniformly chosen point in the original triangle we...
How do I import CSV file into a MySQL table?
... MySQL table so that I can refactor into a sane format. I created a table called 'CSVImport' that has one field for every column of the CSV file. The CSV contains 99 columns , so this was a hard enough task in itself:
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What is the definition of “interface” in object oriented programming
... one of the more overloaded and confusing terms in development.
It is actually a concept of abstraction and encapsulation. For a given "box", it declares the "inputs" and "outputs" of that box. In the world of software, that usually means the operations that can be invoked on the box (along with ar...