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When should I use nil and NULL in Objective-C?
...ith an object.
if(str==nil)
NSLog("str is empty");
Now NULL is used for non-object pointer (like a C pointer) in Objective-C. Like nil , NULL got no value nor address.
char *myChar = NULL;
struct MyStruct *dStruct = NULL;
So if there is a situation, when I need to check my struct (structur...
What is the difference between old style and new style classes in Python?
...a
new-style class instance is permitted to override the value returned
for x.__class__).
The major motivation for introducing new-style classes is to provide a unified object model with a full meta-model.
It also has a number of immediate benefits, like the ability to
subclass most ...
Why can't I use a list as a dict key in python?
I'm a bit confused about what can/can't be used as a key for a python dict.
11 Answers
...
Where should signal handlers live in a django project?
...se remote events? The question is how to ensure the listeners are loaded before the emitters.
– John Mee
May 4 '11 at 2:02
...
UICollectionView Set number of columns
...greater control over the layout of your UICollectionView, without the need for subclassing it:
collectionView:layout:insetForSectionAtIndex:
collectionView:layout:minimumInteritemSpacingForSectionAtIndex:
collectionView:layout:minimumLineSpacingForSectionAtIndex:
collectionView:layout:referenceSiz...
C++及Windows异常处理(try，catch; __try,__finally, __except) - C/C++ - ...
...id f(const char* fn)
{
File_handle f(fn,"rw"); // open fn for reading and writing
// use file through f
}
在一个系统中，每一样资源都需要一个“资源局柄”对象，但我们不必为每一个资源都写一个“finally”语句。在实作的系...
Python mysqldb: Library not loaded: libmysqlclient.18.dylib
I just compiled and installed mysqldb for python 2.7 on my mac os 10.6. I created a simple test file that imports
15 Answe...
How to check BLAS/LAPACK linkage in NumPy and SciPy?
...
The method numpy.show_config() (or numpy.__config__.show()) outputs information about linkage gathered at build time. My output looks like this. I think it means I am using the BLAS/LAPACK that ships with Mac OS.
>>> import numpy as np
>>> np.show_config()
lapack_opt_info:
...
What is the difference between join and merge in Pandas?
...
pandas.merge() is the underlying function used for all merge/join behavior.
DataFrames provide the pandas.DataFrame.merge() and pandas.DataFrame.join() methods as a convenient way to access the capabilities of pandas.merge(). For example, df1.merge(right=df2, ...) is eq...
What is the most effective way for float and double comparison?
...n in an algorithm that if a==b and b==c then a==c.
Using the same epsilon for lines measured in inches and lines measured in mils (.001 inch). That is a==b but 1000a!=1000b. (This is why AlmostEqual2sComplement asks for the epsilon or max ULPS).
The use of the same epsilon for both the cosine of an...