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How to add column if not exists on PostgreSQL?
...statement:
DO $$
BEGIN
BEGIN
ALTER TABLE <table_name> ADD COLUMN <column_name> <column_type>;
EXCEPTION
WHEN duplicate_column THEN RAISE NOTICE 'column <column_name> already exists in <table_name>.';
END;
END;
$$
...
What belongs in an educational tool to demonstrate the unwarranted assumptions people make in C/C++?
...)<sizeof(int)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
..25 pointer arithmetic works outside arrays
but '(diff=&var.int2-&var.int1, &var.int1+diff==&var.int2)' is false.
From what I can say with my puny test cases, you are Stop at...
Proper use of beginBackgroundTaskWithExpirationHandler
...ed.
Mine tend look something like this:
- (void) doUpdate
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self beginBackgroundUpdateTask];
NSURLResponse * response = nil;
NSError * error = nil;
NSData * responseData = [NSU...
Encrypt & Decrypt using PyCrypto AES 256
...rt Random
from Crypto.Cipher import AES
class AESCipher(object):
def __init__(self, key):
self.bs = AES.block_size
self.key = hashlib.sha256(key.encode()).digest()
def encrypt(self, raw):
raw = self._pad(raw)
iv = Random.new().read(AES.block_size)
...
Run an Application in GDB Until an Exception Occurs
...case of GNU C++, exceptions are raised by calling a library function named __raise_exception which has the following ANSI C interface:
/* addr is where the exception identifier is stored.
id is the exception identifier. */
void __raise_exception (void **addr, void *id);
To make the debugger c...
How to dynamically create a class?
...rtyType)
{
FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);
PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
MethodBuilder getPropMt...
How to read if a checkbox is checked in PHP?
...="value1">
After submitting the form you can check it with:
isset($_POST['test'])
or
if ($_POST['test'] == 'value1') ...
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Using Django time/date widgets in custom form
... the proper field names from your model):
from django import forms
from my_app.models import Product
from django.contrib.admin import widgets
class ProductForm(forms.ModelForm):
class Meta:
model = Product
def __init__(self, *args, **kwargs):
...
Explicitly calling return in a function or not
...t return. The following plot is created from data selected this way:
bench_nor2 <- function(x,repeats) { system.time(rep(
# without explicit return
(function(x) vector(length=x,mode="numeric"))(x)
,repeats)) }
bench_ret2 <- function(x,repeats) { system.time(rep(
# with explicit return
(funct...
How to get string objects instead of Unicode from JSON?
...
A solution with object_hook
import json
def json_load_byteified(file_handle):
return _byteify(
json.load(file_handle, object_hook=_byteify),
ignore_dicts=True
)
def json_loads_byteified(json_text):
return _byteify(
...