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differentiate null=True, blank=True in django
...o need your database to allow NULL values for that field. The exception is CharFields and TextFields, which in Django are never saved as NULL. Blank values are stored in the DB as an empty string ('').
A few examples:
models.DateTimeField(blank=True) # raises IntegrityError if blank
models.DateTi...
Pandas every nth row
...] # Excludes every 3rd row starting from 0
df2 = df[df.index % 3 == 0] # Selects every 3rd raw starting from 0
This arithmetic based sampling has the ability to enable even more complex row-selections.
This assumes, of course, that you have an index column of ordered, consecutive, integers star...
Mongoose populate after save
... post.populate('group', 'name').populate({
path: 'wallUser',
select: 'name picture'
}, function(err, doc) {
res.json(doc);
});
});
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...
XML attribute vs XML element
...as a > or < you XML document will break I think there are five ascii chars (>, <, &, ?,") that will kill it. If this special character was in an Element you can simply add some CDATA tags around this data. I would say, only use attributes when you 100% know what values are going t...
How to evaluate a math expression given in string form?
...r) {
return new Object() {
int pos = -1, ch;
void nextChar() {
ch = (++pos < str.length()) ? str.charAt(pos) : -1;
}
boolean eat(int charToEat) {
while (ch == ' ') nextChar();
if (ch == charToEat) {
nextChar...
What's the best way to check if a file exists in C?
...t; // stat
#include <stdbool.h> // bool type
bool file_exists (char *filename) {
struct stat buffer;
return (stat (filename, &buffer) == 0);
}
and call it like this:
#include <stdio.h> // printf
int main(int ac, char **av) {
if (ac != 2)
return 1;
...
Improve INSERT-per-second performance of SQLite
...ple threads (connection per-thread).
First find the items, in the table:
SELECT COUNT(*) FROM table
then read in pages (LIMIT/OFFSET):
SELECT * FROM table ORDER BY _ROWID_ LIMIT <limit> OFFSET <offset>
where and are calculated per-thread, like this:
int limit = (count + n_threa...
Programmatically open new pages on Tabs
... When the "Let Internet Explorer decide how popups open" option is selected, what criteria does Internet Explorer use to make this decision?
– Dead.Rabit
Apr 7 '16 at 7:45
...
Get element inside element by class and ID - JavaScript
...
Well, first you need to select the elements with a function like getElementById.
var targetDiv = document.getElementById("foo").getElementsByClassName("bar")[0];
getElementById only returns one node, but getElementsByClassName returns a node list...
jQuery.parseJSON throws “Invalid JSON” error due to escaped single quote in JSON
...o the state machine diagram on the JSON website, only escaped double-quote characters are allowed, not single-quotes. Single quote characters do not need to be escaped:
Update - More information for those that are interested:
Douglas Crockford does not specifically say why the JSON specificat...