[Numpy-discussion] numpy.genfromtxt converters issue

Pierre GM pgmdevlist@gmail....
Thu Nov 11 12:21:48 CST 2010

Sorry for the delayed answer. I had a bit of time and examined the issue in more details:

As you've seen, the output of your converter is not detected as a float, but as an object. That's an unfortunate side effect of using a lambda function such as yours: what if your input string has only 1 character ? You end up taking the float of an empty string, which raises a ValueError.
In practice, that's exactly what happens below the hood when genfromtxt tries to guess the output type of the converter. It tries a single value ('1'), fails, and decides that the result must be an object... Probably not the best strategy, as it crashes in your case. But yours is a buggy case anyway.

Try that instead of your lambda function
def func(s):
        r = float(s[1:])
    except ValueError:
        r = 1.
    return r

You could object that as the dtype is defined, it should take precedence over the output typeof the converter. Well, I assumed exactly the opposite: if the user took the time to define a converter, we should respect his/her choice and overwrite the dtype.

Now, we can argue over the very last point: if both a converter and a dtype are specified, which one should take precedence?
You have my opinion, let's hear yours.

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