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MongoDB/NoSQL: Keeping Document Change History
... changes to one or more specific entities in a database. I've heard this called row versioning, a log table or a history table (I'm sure there are other names for it). There are a number of ways to approach it in an RDBMS--you can write all changes from all source tables to a single table (more of...
Efficient way to apply multiple filters to pandas DataFrame or Series
...s to apply several filters to a Pandas DataFrame or Series object. Essentially, I want to efficiently chain a bunch of filtering (comparison operations) together that are specified at run-time by the user.
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urllib2.HTTPError: HTTP Error 403: Forbidden
...Error, e:
print e.fp.read()
content = page.read()
print content
Actually, it works with just this one additional header:
'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
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Why was “Avoid Enums Where You Only Need Ints” removed from Android's performance tips?
...ume that a developer is only adding enums where they're useful. The only really bad use I've seen of enums was in some harmony code where they really wanted ints (for bitmasks and the like) and the "enum" wasn't an enum in any reasonable sense. If you find yourself calling "ordinal()" a lot, that's ...
Is there a generator version of `string.split()` in Python?
...plitlines chops off the trainling newline though (something that I don't really like...); if you wanted to replicated that part of the behavior, you could use grouping: (m.group(2) or m.group(3) for m in re.finditer('((.*)\n|(.+)$)', s)). PS: I guess the outer paren in the RE are not needed; I just ...
In Scala, what exactly does 'val a: A = _' (underscore) mean?
....0d if T is Double,
false if T is Boolean,
() if T is Unit,
null for all other types T.
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How do I specify different Layouts in the ASP.NET MVC 3 razor ViewStart file?
... One potential problem with LayoutInjecterAttribute: It is called before the controller's OnException method. So, if the controller provides a view result during exception handling, the layout won't be set.
– Jeff Sharp
Apr 21 '14 at 17:03
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Run an Application in GDB Until an Exception Occurs
... a C++ exception.
catch
The catching of a C++ exception.
exec
A call to exec. This is currently only available for HP-UX.
fork
A call to fork. This is currently only available for HP-UX.
vfork
A call to vfork. This is currently only available for HP-UX.
load or load libname
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Python memory leaks [closed]
... have a long-running script which, if let to run long enough, will consume all the memory on my system.
9 Answers
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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...