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Swapping column values in MySQL
...t. This method doesn't swap the values if one of them is NULL. Use method #3 that doesn't have this limitation.
UPDATE swap_test SET x=y, y=@temp WHERE (@temp:=x) IS NOT NULL;
This method was offered by Dipin in, yet again, the comments of http://beerpla.net/2009/02/17/swapping-column-values-in-mys...
how to concatenate two dictionaries to create a new one in Python? [duplicate]
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Slowest and doesn't work in Python3: concatenate the items and call dict on the resulting list:
$ python -mtimeit -s'd1={1:2,3:4}; d2={5:6,7:9}; d3={10:8,13:22}' \
'd4 = dict(d1.items() + d2.items() + d3.items())'
100000 loops, best of 3: 4.93 usec per loop...
Move the most recent commit(s) to a new branch with Git
... existingbranch
git merge master
git checkout master
git reset --hard HEAD~3 # Go back 3 commits. You *will* lose uncommitted work.
git checkout existingbranch
Moving to a new branch
WARNING: This method works because you are creating a new branch with the first command: git branch newbranch. If yo...
Int division: Why is the result of 1/3 == 0?
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The two operands (1 and 3) are integers, therefore integer arithmetic (division here) is used. Declaring the result variable as double just causes an implicit conversion to occur after division.
Integer division of course returns the true result of...
Is passing 'this' in a method call accepted practice in java
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answered Jul 3 '13 at 7:16
Denys SéguretDenys Séguret
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Get difference between two lists
...))
Out[5]: ['Four', 'Three']
Beware that
In [5]: set([1, 2]) - set([2, 3])
Out[5]: set([1])
where you might expect/want it to equal set([1, 3]). If you do want set([1, 3]) as your answer, you'll need to use set([1, 2]).symmetric_difference(set([2, 3])).
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How to count the frequency of the elements in an unordered list?
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33 Answers
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Is there a difference between using a dict literal and a dict constructor?
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answered Jul 7 '11 at 12:43
John La RooyJohn La Rooy
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How to print a dictionary line by line in Python?
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13 Answers
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...到 1 个顶层表达式
[2:01:15 PM] [YAIL] 执行[0]: (begin ...) len=3
[2:01:15 PM] [YAIL] begin: 2 个子表达式
[2:01:15 PM] [YAIL] begin[1]: (require) len=2
[2:01:15 PM] [YAIL] begin[2]: (process-repl-input) len=3
[2:01:15 PM] [YAIL] begin: 1 个子表...