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In pure functional languages, is there an algorithm to get the inverse function?
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In some cases, yes! There's a beautiful paper called Bidirectionalization for Free! which discusses a few cases -- when your function is sufficiently polymorphic -- where it is possible, completely automatically to derive an inverse function. (It also discusses what makes...
wkhtmltopdf: cannot connect to X server
...ble, so no need to make the wrapper script.
– jeffery_the_wind
Mar 13 '12 at 13:43
it worked for me.. in some situatio...
Exif manipulation library for python [closed]
...mation from Jpeg and Tiff files which include it. This information is typically included in images created using digital imaging devices such as digital cameras, digital film scanners, etc.
However, it looks like pyexif hasn't been updated in quite while. They recommend if theirs isn't doing the ...
PHP: exceptions vs errors?
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Exceptions are thrown - they are intended to be caught. Errors are generally unrecoverable. Lets say for instance - you have a block of code that will insert a row into a database. It is possible that this call fails (duplicate ID) - you will want to have a "Error" which in this case is an "Exc...
What is the difference between dict.items() and dict.iteritems() in Python2?
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It's part of an evolution.
Originally, Python items() built a real list of tuples and returned that. That could potentially take a lot of extra memory.
Then, generators were introduced to the language in general, and that method was reimplemented as an ite...
Why do we use __init__ in Python classes?
...Spot is a bit of a cripple and is mostly yellow. The __init__ function is called a constructor, or initializer, and is automatically called when you create a new instance of a class. Within that function, the newly created object is assigned to the parameter self. The notation self.legs is an attrib...
How to read keyboard-input?
... mixing different Pythons here (Python 2.x vs. Python 3.x)...
This is basically correct:
nb = input('Choose a number: ')
The problem is that it is only supported in Python 3. As @sharpner answered, for older versions of Python (2.x), you have to use the function raw_input:
nb = raw_input('Choose...
Can someone explain the traverse function in Haskell?
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traverse is the same as fmap, except that it also allows you to run effects while you're rebuilding the data structure.
Take a look at the example from the Data.Traversable documentation.
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
The Functor instance of Tr...
How to set custom favicon in Express?
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In Express 4
Install the favicon middleware and then do:
var favicon = require('serve-favicon');
app.use(favicon(__dirname + '/public/images/favicon.ico'));
Or better, using the path module:
app.use(favicon(path.join(__dirname,'public','ima...
Fastest method to replace all instances of a character in a string [duplicate]
What is the fastest way to replace all instances of a string/character in a string in JavaScript? A while , a for -loop, a regular expression?
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