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How does deriving work in Haskell?
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The short answer is, magic :-). This is to say that automatic deriving is baked into the Haskell spec, and every compiler can choose to implement it in its own way. There's lots of work on how to make it extensible however.
Derive...
In Python, how do I read the exif data for an image?
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You can use the _getexif() protected method of a PIL Image.
import PIL.Image
img = PIL.Image.open('img.jpg')
exif_data = img._getexif()
This should give you a dictionary indexed by EXIF numeric tags. If you want the dictionary indexed by the actual EXIF tag name strings, try something ...
Spring Test & Security: How to mock authentication?
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Seaching for answer I couldn't find any to be easy and flexible at the same time, then I found the Spring Security Reference and I realized there are near to perfect solutions. AOP solutions often are the greatest ones for testing, and...
HTML span align center not working?
...as a CSS property. Align is an attribute.
<span align="center" style="border:1px solid red;">
This is some text in a div element!
</span>
However, the align attribute is deprecated. You should use the CSS text-align property on the container.
<div style="text-align: center;"&g...
Javascript: How to generate formatted easy-to-read JSON straight from an object? [duplicate]
I know how to generate JSON from an object using JSON.stringify, or in my case the handy jquery-json from google code ( https://github.com/krinkle/jquery-json ).
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Pass column name in data.table using variable [duplicate]
...# [1] "b" "b" "b" "a" "a"
With a single column name, the result is a vector. If you want a data.table result, or several columns, use list form
temp <- quote(list(x, v))
DT[ , eval(temp)]
# x v
# 1: b 1.52566586
# 2: b 0.66057253
# 3: b -1.29654641
# 4: a -1.71998260
# 5: a 0.03...
What does %>% mean in R [duplicate]
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The infix operator %>% is not part of base R, but is in fact defined by the package magrittr (CRAN) and is heavily used by dplyr (CRAN).
It works like a pipe, hence the reference to Magritte's famous painting The Treachery of Images.
Wh...
Node.js Error: Cannot find module express
...ur application (node_modules folder):
$ npm install express
The reason for this is that applications always look in their local context for any dependencies. The global installation is only for setting up system-wide available binaries, such as unit test runners or bootstrappers or things like th...
What does -> mean in Python function definitions?
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It's a function annotation.
In more detail, Python 2.x has docstrings, which allow you to attach a metadata string to various types of object. This is amazingly handy, so Python 3 extends the feature by allowing you to attach metadata to functions describin...
pyplot scatter plot marker size
In the pyplot document for scatter plot:
6 Answers
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