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List of lists changes reflected across sublists unexpectedly
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When you write [x]*3 you get, essentially, the list [x, x, x]. That is, a list with 3 references to the same x. When you then modify this single x it is visible via all three references to it:
x = [1] * 4
l = [x] * 3
print(f"id(x): {id(x)}")
# id(x): 1405608979...
Why are preprocessor macros evil and what are the alternatives?
I have always asked this but I have never received a really good answer; I think that almost any programmer before even writing the first "Hello World" had encountered a phrase like "macro should never be used", "macro are evil" and so on, my question is: why? With the new C++11 is there a real alte...
How to think in data stores instead of databases?
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The datastore makes no distinction between inserts and updates. When you call put() on an entity, that entity gets stored to the datastore with its unique key, and anything that has that key gets overwritten. Basically, each entity kind in the datastore acts like an enormous map or sorted list.
Que...
Importing from a relative path in Python
...his method is still commonly used in some situations, where you aren't actually ever 'installing' your package. For example, it's popular with Django users.
You can add Common/ to your sys.path (the list of paths python looks at to import things):
import sys, os
sys.path.append(os.path.join(os.p...
How to clear MemoryCache?
...clear it first. What is the quickest way to do this? Should I loop through all the items and remove them one at a time or is there a better way?
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Test PHP headers with PHPUnit
...78
Error: Class 'PHPUnit_Util_Configuration' not found in - on line 378
Call Stack:
0.0013 582512 1. {main}() -:0
Try add this to your bootstrap file to fix it:
<?php
if (!defined('PHPUNIT_COMPOSER_INSTALL')) {
define('PHPUNIT_COMPOSER_INSTALL', __DIR__ . '/path/to/composer/ven...
Is there a way to make npm install (the command) to work behind proxy?
...roxy variable in a .npmrc file but it does not work. Trying to avoid manually downloading all require packages and installing.
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Error: No default engine was specified and no extension was provided
...err }); lines in your code with:
res.json({ error: err })
PS: People usually also have message in the returned object:
res.status(err.status || 500);
res.json({
message: err.message,
error: err
});
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How to redirect to a 404 in Rails?
...ou want to show a 404 page, create a render_404 method (or not_found as I called it) in ApplicationController like this:
def not_found
raise ActionController::RoutingError.new('Not Found')
end
Rails also handles AbstractController::ActionNotFound, and ActiveRecord::RecordNotFound the same way....
How to create a DataTable in C# and how to add rows?
...ma/structure, do:
dt.WriteXMLSchema("dtSchemaOrStructure.xml");
Additionally, you can also export your data:
dt.WriteXML("dtDataxml");
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