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How to initialize all members of an array to the same value?
...e same value, without multiple copy-paste, you can use macros:
#define VAL_1X 42
#define VAL_2X VAL_1X, VAL_1X
#define VAL_4X VAL_2X, VAL_2X
#define VAL_8X VAL_4X, VAL_4X
#define VAL_16X VAL_8X, VAL_8X
#define VAL_32X VAL_16X, VAL_16X
#define VAL_64X VAL_32X, VAL_32X
i...
Python != operation vs “is not”
...ght hand side and the left hand side are equal objects (according to their __eq__ or __cmp__ methods.)
is is an identity test. It checks whether the right hand side and the left hand side are the very same object. No methodcalls are done, objects can't influence the is operation.
You use is (and i...
How to apply a function to two columns of Pandas dataframe
Suppose I have a df which has columns of 'ID', 'col_1', 'col_2' . And I define a function :
12 Answers
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std::function and std::bind: what are they, and when should they be used?
...ere are two left to go.
You can use std::bind to get g:
auto g = bind(f, _1, 4, _2);
This is more concise than actually writing a functor class to do it.
There are further examples in the article you link to. You generally use it when you need to pass a functor to some algorithm. You have a fun...
What's a correct and good way to implement __hash__()?
What's a correct and good way to implement __hash__() ?
6 Answers
6
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Why does Python code use len() function instead of a length method?
...
Strings do have a length method: __len__()
The protocol in Python is to implement this method on objects which have a length and use the built-in len() function, which calls it for you, similar to the way you would implement __iter__() and use the built-in ...
How can I create a copy of an object in Python?
... get a copy method (in 2, you'd use a slice to make a copy):
>>> a_list = list('abc')
>>> a_copy_of_a_list = a_list.copy()
>>> a_copy_of_a_list is a_list
False
>>> a_copy_of_a_list == a_list
True
Shallow Copies
Shallow copies are just copies of the outermost cont...
Extract traceback info from an exception object
...n you're using.
In Python 3
It's simple: exceptions come equipped with a __traceback__ attribute that contains the traceback. This attribute is also writable, and can be conveniently set using the with_traceback method of exceptions:
raise Exception("foo occurred").with_traceback(tracebackobj)
...
Python: Bind an Unbound Method?
...
All functions are also descriptors, so you can bind them by calling their __get__ method:
bound_handler = handler.__get__(self, MyWidget)
Here's R. Hettinger's excellent guide to descriptors.
As a self-contained example pulled from Keith's comment:
def bind(instance, func, as_name=None):
...
Why is __init__() always called after __new__()?
...
Use __new__ when you need to control
the creation of a new instance.
Use
__init__ when you need to control initialization of a new instance.
__new__ is the first step of instance creation. It's called first, and i...