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List changes unexpectedly after assignment. How do I clone or copy it to prevent this?
While using new_list = my_list , any modifications to new_list changes my_list everytime. Why is this, and how can I clone or copy the list to prevent it?
...
C# Lazy Loaded Automatic Properties
... 4.0 Lazy<T> type to create this pattern
private Lazy<string> _someVariable =new Lazy<string>(SomeClass.IOnlyWantToCallYouOnce);
public string SomeVariable => _someVariable.Value;
This code will lazily calculate the value of _someVariable the first time the Value expression i...
error: ‘uint16_t’ does not name a type - C/C++ - 清泛网 - 专注C/C++及内核技术
error: ‘uint16_t’ does not name a type#include <stdint.h> 解决。 ** * @file stdint.h * Copyright 2012, 2013 MinGW.org project * * Permission is hereby ...#include <stdint.h> 解决。
/**
* @file stdint.h
* Copyright 2012, 2013 MinGW.org project
*
* Permission is hereby granted, ...
Does reading an entire file leave the file handle open?
...file is closed, is this pattern:
with open('Path/to/file', 'r') as content_file:
content = content_file.read()
which will always close the file immediately after the block ends; even if an exception occurs.
Edit: To put a finer point on it:
Other than file.__exit__(), which is "automatical...
How to JSON serialize sets?
I have a Python set that contains objects with __hash__ and __eq__ methods in order to make certain no duplicates are included in the collection.
...
Clean code to printf size_t in C++ (or: Nearest equivalent of C99's %z in C++)
I have some C++ code that prints a size_t :
9 Answers
9
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What is the fastest way to check if a class has a function defined?
...tr() to get the attribute, and callable() to verify it is a method:
invert_op = getattr(self, "invert_op", None)
if callable(invert_op):
invert_op(self.path.parent_op)
Note that getattr() normally throws exception when the attribute doesn't exist. However, if you specify a default value (None...
How does Django's Meta class work?
...n [2]: User.Meta
Out[2]: django.contrib.auth.models.Meta
In [3]: User.Meta.__dict__
Out[3]:
{'__doc__': None,
'__module__': 'django.contrib.auth.models',
'abstract': False,
'verbose_name': <django.utils.functional.__proxy__ at 0x26a6610>,
'verbose_name_plural': <django.utils.functional...
Use of #pragma in C
... == 7
Here's how you'd do the same thing in GCC:
struct PackedStructure __attribute__((__packed__))
{
char a;
int b;
short c;
};
// sizeof(PackedStructure == 7)
The GCC code is more portable, because if you want to compile that with a non-GCC compiler, all you have to do is
#define __att...
sqlalchemy unique across multiple columns
... declares those in the table definition, or if using declarative as in the __table_args__:
# version1: table definition
mytable = Table('mytable', meta,
# ...
Column('customer_id', Integer, ForeignKey('customers.customer_id')),
Column('location_code', Unicode(10)),
UniqueConstraint...