Tang's DW

Nifty link of the nonce

2014-05-14T16:47:17Z

"Why Python Is Slow" is a quick read on Python's dynamic typing. I had not known that it was possible to change the value of an integer constant in Python.

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Proprietary Value Decomposition

2014-04-09T03:43:49Z

Math has a concept called singular value decomposition. The short version is that you put in one matrix and get three out. This apparently being a well known concept in engineering, it is implemented in the data analysis language IDL and in the NumPY library for Python, and you can probably guess where this is going. The singular value decomposition functions in IDL and NumPy produce different matrices for the same input matrix.

All three output matrices have their columns swapped.
One of the columns in the 'u' matrix is the negative of the matching column in the other language.
One of the rows in the 'v' matrix is the negative of the matching row in the other language.

I've only tested one chunk of data, so I do not know if the pattern will hold for different input matrices.

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Obscure bug of the nonce

2014-03-23T13:44:38Z

Python easy_install on Windows sometimes fails with a UnicodeDecodeError:

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 6034: ordinal not in range(128)

The solution is to comment out the config = config.decode('ascii') line in Lib/site-packages/setuptools/easy_install.py.

Here's an even more fun one:

  File "geopts.py", line 128, in xp2str
    s = etree.tostring(resultset[0], method="text")
  File "lxml.etree.pyx", line 3165, in lxml.etree.tostring (src\lxml\lxml.etree.
c:69399)

exceptions.TypeError: Type '_ElementStringResult' cannot be serialized.

This says that the XML library's own tostring() function cannot convert one of its own string types to a string. What's especially brilliant about this is that _ElementStringResult inherits from the native string class.

Here is a hacky attempt to manage the problem:

r = resultset[0]
if isinstance(r, etree._ElementStringResult):
    s = r
else:
    s = etree.tostring(r, method="text")

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easy_fail_to_install

2014-03-19T00:31:13Z

This is only my opinion fwiw, but library/add-on packages for a high-level scripting language should not require a C compiler, any version of Visual Studio, or any development environment for any different lower-level language.

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Scrap dump: Key handling in PyGame

2012-08-31T07:12:31Z

Some notes on keypress handling in Python's PyGame library, from about seven years ago: ( Read more... )

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