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MySQL Conditional Insert
... DBMS does not impose limitations on which table you select from when you execute an insert, try:
INSERT INTO x_table(instance, user, item)
SELECT 919191, 123, 456
FROM dual
WHERE NOT EXISTS (SELECT * FROM x_table
WHERE user = 123
...
What's the difference between a proxy server and a reverse proxy server? [closed]
What is the difference between a proxy server and a reverse proxy server?
21 Answers
2...
How to apply a function to two columns of Pandas dataframe
...
Here's an example using apply on the dataframe, which I am calling with axis = 1.
Note the difference is that instead of trying to pass two values to the function f, rewrite the function to accept a pandas Series object, and then inde...
Is gcc's __attribute__((packed)) / #pragma pack unsafe?
...entially unsafe on some systems. The symptom probably won't show up on an x86, which just makes the problem more insidious; testing on x86 systems won't reveal the problem. (On the x86, misaligned accesses are handled in hardware; if you dereference an int* pointer that points to an odd address, i...
numpy: most efficient frequency counts for unique values in an array
....org/doc/numpy/reference/generated/numpy.bincount.html
import numpy as np
x = np.array([1,1,1,2,2,2,5,25,1,1])
y = np.bincount(x)
ii = np.nonzero(y)[0]
And then:
zip(ii,y[ii])
# [(1, 5), (2, 3), (5, 1), (25, 1)]
or:
np.vstack((ii,y[ii])).T
# array([[ 1, 5],
[ 2, 3],
[ 5, ...
Ternary Operators in JavaScript Without an “Else”
...
First of all, a ternary expression is not a replacement for an if/else construct - its an equivalent to an if/else construct that returns a value. That is, an if/else clause is code, a ternary expression is an expression, meaning that it returns a va...
Why does the expression 0 < 0 == 0 return False in Python?
...g for sequences of relational operators to make range comparisons easy to express. It's much nicer to be able to say 0 < x <= 5 than to say (0 < x) and (x <= 5).
These are called chained comparisons. And that's a link to the documentation for them.
With the other cases you talk about, ...
Are the shift operators () arithmetic or logical in C?
...ifting a signed value, the >> operator is an arithmetic shift.
For example, assuming a 32 bit machine:
signed int x1 = 5;
assert((x1 >> 1) == 2);
signed int x2 = -5;
assert((x2 >> 1) == -3);
unsigned int x3 = (unsigned int)-5;
assert((x3 >> 1) == 0x7FFFFFFD);
...
How to convert a string of bytes into an int?
... use the struct module to do this:
>>> struct.unpack("<L", "y\xcc\xa6\xbb")[0]
3148270713L
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