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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
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144
To clarify on the "This is bad" - you could get all the wheels with 1 select (SELECT * from Wheel;), instead of N+1. With a large N, the pe...
Why are Python lambdas useful? [closed]
...ions to do stuff. Example:
mult3 = filter(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, 6, 7, 8, 9])
sets mult3 to [3, 6, 9], those elements of the original list that are multiples of 3. This is shorter (and, one could argue, clearer) than
def filterfunc(x):
return x % 3 == 0
mult3 = filter(filterfu...
NerdTree - Reveal file in tree
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ThomasThomas
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correct way to use super (argument passing)
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edited Jan 23 '12 at 19:40
answered Jan 23 '12 at 14:39
u...
Why is it slower to iterate over a small string than a small list?
...thon3 -m timeit '[x for x in ["a", "b", "c"]]'
1000000 loops, best of 3: 0.436 usec per loop
This disagrees with what you've found...
You must be using Python 2, then.
>>> python2 -m timeit '[x for x in "abc"]'
1000000 loops, best of 3: 0.309 usec per loop
>>> python2 -m timei...
Making an array of integers in iOS
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You can use a plain old C array:
NSInteger myIntegers[40];
for (NSInteger i = 0; i < 40; i++)
myIntegers[i] = i;
// to get one of them
NSLog (@"The 4th integer is: %d", myIntegers[3]);
Or, you can use an NSArray or NSMutableArray, but here you will need to wrap up eac...
How to keep index when using pandas merge
...1 1 1
b 2 3 2
c 3 4 NaN
Note that for some left merge operations, you may end up with more rows than in a when there are multiple matches between a and b. In this case, you may need to drop duplicates.
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Xcode 4 - build output directory
I have problems with setting up/locating my output files in Xcode4 (beta 5). They are placed somewhere in ~/Library/Developer/ugly_path/... . I can't even select "show in finder" on my products. It is the same for a simple C project, Foundation tool and even Cocoa bundle. A Debugging works fine.
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How to validate an email address in PHP
...\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22)))*@(?:(?:(?!.*[^.]{64,})(?:(?:(?:xn--)?[a-z0-9]+(?:-+[a-z0-9]+)*\\.){1,126}){1,}(?:(?:[a-z][a-z0-9]*)|(?:(?:xn--)[a-z0-9]+))(?:-+[a-z0-9]+)*)|(?:\\[(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})|(?:(?!(?:.*[a-f0-9][:\\]]){7,})(?:[a-f0-9]{1...