On Sun, Oct 17, 2010 at 5:35 PM, braingateway <braingate...@gmail.com>wrote:
> Hi Everyone,
>
> I am trying the matplotlib. I have to say this is a powerful package for
> scientific 2-D plotting. However, I encountered some problems when try
> to generate several colormaps.
>
> for example:
> a=cm.get_cmap('gist_rainbow',256)(range(256))
> will give a error:
> Traceback (most recent call last):
> File "<pyshell#82>", line 1, in <module>
> a=cm.get_cmap('gist_rainbow',256)(range(256))
> File "...\site-packages\matplotlib\colors.py", line 498, in __call__
> if not self._isinit: self._init()
> File "...\site-packages\matplotlib\colors.py", line 649, in _init
> self._segmentdata['red'], self._gamma)
> TypeError: tuple indices must be integers, not str
>
> but other colormaps can actually work:
> a=cm.get_cmap('gist_stern',256)(range(256))
> >>> a
> array([[ 0. , 0. , 0. , 1. ],
> [ 0.0716923 , 0.00392157, 0.00784314, 1. ],
> [ 0.14338459, 0.00784314, 0.01568627, 1. ],
> ...,
> [ 0.99215686, 0.99215686, 0.97040326, 1. ],
> [ 0.99607843, 0.99607843, 0.98520163, 1. ],
> [ 1. , 1. , 1. , 1. ]])
>
> I tried all possible colormaps and found out: gist_rainbow, terrain,
> bwr, brg, and seismic will generate the same error, all other colormaps
> are OK. I wonder is this a bug or expected behavior?
> ###############################
> ##matplotlib verison : '1.0.svn'
> >>> maps=[m for m in cm.datad if not m.endswith("_r")]
> >>> for i in maps:
> try:
> a=cm.get_cmap(i,256)(range(256))
> except:
> (type, value, traceback) = sys.exc_info()
> print "Problems to create %s" % (i,)
> print "The error was --> %s: %s" % (type, value)
>
>
> Problems to create gist_rainbow
> The error was --> <type 'exceptions.TypeError'>: tuple indices must be
> integers, not str
> Problems to create terrain
> The error was --> <type 'exceptions.TypeError'>: tuple indices must be
> integers, not str
> Problems to create bwr
> The error was --> <type 'exceptions.TypeError'>: tuple indices must be
> integers, not str
> Problems to create brg
> The error was --> <type 'exceptions.TypeError'>: tuple indices must be
> integers, not str
> Problems to create seismic
> The error was --> <type 'exceptions.TypeError'>: tuple indices must be
> integers, not str
> ##################################################################
>
>
Is there any particular reason why you are doing the "(range(256))"? Keep
in mind that a colormap in matplotlib works differently than a colormap in
Matlab. In Matlab, the colormap is a 2-D array of rgb values, while in
matplotlib, it is an object that is used by the backends for
color-rendering.
Often times, you will not need to do anything more than specify which
colormap you want by name e.g., pcolor(X, Y, Z, cmap='gist_rainbow'), or by
passing in a customized or self-made colormap object to the 'cmap' keyword
argument.
What is happening in your code when you call '(range(256))' is that the
colormap is being called for an array of values ranging from 0 to 255 and
is determining what the color will be for each of those values. What seems
to be happening with those few colormaps is that the call is being made
before those maps are properly self-initialized. So, there might be some
sort of flaw here that you have exposed, but I would suggest taking another
look at what you are trying to accomplish to see if there is a better way.
Thanks for giving matplotlib a try and I hope you continue to use it for
your work!
Ben Root
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