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What is the “__v” field in Mongoose
I'm using Mongoose version 3 with MongoDB version 2.2. I've noticed a __v field has started appearing in my MongoDB documents. Is it something to do with versioning? How is it used?
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How does functools partial do what it does?
...unction (a callable, to be precise) that behaves like sum2, but has one positional argument less. That missing argument is always substituted by 4, so that partial(sum2, 4)(2) == sum2(4, 2)
As for why it's needed, there's a variety of cases. Just for one, suppose you have to pass a function somewhe...
Principal component analysis in Python
I'd like to use principal component analysis (PCA) for dimensionality reduction. Does numpy or scipy already have it, or do I have to roll my own using numpy.linalg.eigh ?
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How do I find the location of my Python site-packages directory?
How do I find the location of my site-packages directory?
21 Answers
21
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Forward an invocation of a variadic function in C
In C, is it possible to forward the invocation of a variadic function? As in,
12 Answers
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Threading pool similar to the multiprocessing Pool?
...y is a thread-based Pool interface in the multiprocessing module, however it is hidden somewhat and not properly documented.
It can be imported via
from multiprocessing.pool import ThreadPool
It is implemented using a dummy Process class wrapping a python thread. This thread-based Process clas...
List changes unexpectedly after assignment. How do I clone or copy it to prevent this?
...t everytime. Why is this, and how can I clone or copy the list to prevent it?
22 Answers
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Class method decorator with self arguments?
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Yes. Instead of passing in the instance attribute at class definition time, check it at runtime:
def check_authorization(f):
def wrapper(*args):
print args[0].url
return f(*args)
return wrapper
class Client(object):
def __init__(self, url):
self.url =...
How do I change the working directory in Python?
...
You can change the working directory with:
import os
os.chdir(path)
There are two best practices to follow when using this method:
Catch the exception (WindowsError, OSError) on invalid path. If the exception is thrown, do not perform any recursive operati...
What's the difference between a file descriptor and file pointer?
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You pass "naked" file descriptors to actual Unix calls, such as read(), write() and so on.
A FILE pointer is a C standard library-level construct, used to represent a file. The FILE wraps the file descriptor, and adds buffering and other features to make I/O easier.
You pass FILE pointers to stan...