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What exactly does += do in python?
...
In Python, += is sugar coating for the __iadd__ special method, or __add__ or __radd__ if __iadd__ isn't present. The __iadd__ method of a class can do anything it wants. The list object implements it and uses it to iterate over an iterable object appending each...
How to override the [] operator in Python?
...
You need to use the __getitem__ method.
class MyClass:
def __getitem__(self, key):
return key * 2
myobj = MyClass()
myobj[3] #Output: 6
And if you're going to be setting values you'll need to implement the __setitem__ method too,...
Find current directory and file's directory [duplicate]
...ory a Python file is contained in, write this in that file:
import os
dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relativ...
RuntimeError on windows trying python multiprocessing
...l import (i.e. execute) the main module at start. You need to insert an if __name__ == '__main__': guard in the main module to avoid creating subprocesses recursively.
Modified testMain.py:
import parallelTestModule
if __name__ == '__main__':
extractor = parallelTestModule.ParallelExtrac...
What is a mixin, and why are they useful?
... and `==`,
but this class does NOT implement those methods."""
def __ne__(self, other):
return not (self == other)
def __lt__(self, other):
return self <= other and (self != other)
def __gt__(self, other):
return not self <= other
def __ge__(self, ot...
C Macro definition to determine big endian or little endian machine?
...byte orders, ready to be put into a file called order32.h:
#ifndef ORDER32_H
#define ORDER32_H
#include <limits.h>
#include <stdint.h>
#if CHAR_BIT != 8
#error "unsupported char size"
#endif
enum
{
O32_LITTLE_ENDIAN = 0x03020100ul,
O32_BIG_ENDIAN = 0x00010203ul,
O32_PDP_E...
How do I get the number of elements in a list?
...objects with a "size" in Python, in particular, have an attribute called ob_size, where the number of elements in the object is cached. So checking the number of objects in a list is very fast.
But if you're checking if list size is zero or not, don't use len - instead, put the list in a boolean co...
How do I determine the size of an object in Python?
...rieve the size and would cause a
TypeError.
getsizeof calls the object’s
__sizeof__ method and adds an additional garbage collector overhead
if the object is managed by the
garbage collector.
See recursive sizeof recipe for an example of using getsizeof() recursively to find the size of containers...
How to access outer class from an inner class?
...f):
return Outer.Inner(self)
class Inner(object):
def __init__(self, outer_instance):
self.outer_instance = outer_instance
self.outer_instance.somemethod()
def inner_method(self):
self.outer_instance.anothermethod()
...
【解决】scrapyd启动job时报错：exceptions.TypeError: __init__() got an ...
【解决】scrapyd启动job时报错：exceptions.TypeError: __init__() got an unexpected keyword argument '_job'进入项目spiders目录, 修改 spider py 文件（你自己的spider的主文件）：def __init__(self):改为：def __init__(self, *args, **kwargs):最后不要忘了重新部署一...