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Solving “Who owns the Zebra” programmatically?
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Here's a solution in Python based on constraint-programming:
from constraint import AllDifferentConstraint, InSetConstraint, Problem
# variables
colors = "blue red green white yellow".split()
nationalities = "Norwegian German Dane Swede Engli...
What is an abstract class in PHP?
What is an abstract class in PHP?
7 Answers
7
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u'\ufeff' in Python string
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The Unicode character U+FEFF is the byte order mark, or BOM, and is used to tell the difference between big- and little-endian UTF-16 encoding. If you decode the web page using the right codec, Python will remove it for you. Examples:
#!python2
#coding: utf8...
NameError: name 'self' is not defined
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Default argument values are evaluated at function define-time, but self is an argument only available at function call time. Thus arguments in the argument list cannot refer each other.
It's a common pattern to default an argument to None and add a test for that in code:
def p(self, b=...
What is an initialization block?
We can put code in a constructor or a method or an initialization block. What is the use of initialization block? Is it necessary that every java program must have it?
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Null coalescing in powershell
... you can use the standard Powershell if statements as an expression:
variable = if (condition) { expr1 } else { expr2 }
So to the replacements for your first C# expression of:
var s = myval ?? "new value";
becomes one of the following (depending on preference):
$s = if ($myval -eq $null) { "n...
Combine two or more columns in a dataframe into a new column with a new name
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Use paste.
df$x <- paste(df$n,df$s)
df
# n s b x
# 1 2 aa TRUE 2 aa
# 2 3 bb FALSE 3 bb
# 3 5 cc TRUE 5 cc
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XPath to select multiple tags
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One correct answer is:
/a/b/*[self::c or self::d or self::e]
Do note that this
a/b/*[local-name()='c' or local-name()='d' or local-name()='e']
is both too-long and incorrect. This XPath expression will select nodes like:
OhMy:c
NotWanted:d
Qu...
When NOT to call super() method when overriding?
...ustom class, I extend its native class. Then when I want to override the base method, I always call super() method, just like I always do in onCreate , onStop , etc.
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Call a function from another file?
...te from file import function, and then call the function using function(a, b). The reason why this may not work, is because file is one of Python's core modules, so I suggest you change the name of your file.
Note that if you're trying to import functions from a.py to a file called b.py, you will n...