问题

AIM

I am attempting to:

Create a histogram,
Store it temporary memory,
Pass the image to the template.

I am having trouble with Step 3 above. I suspect that I am making a simple and fundamental error in relation to passing the context data to the template.

ERROR

HTML is rendering with a broken image tag.

CODE

Views.py

class SearchResultsView(DetailView):

   ...

   def get(self, request, *args, **kwargs):
        self.get_histogram(request)
        return super(SearchResultsView, self).get(request, *args, **kwargs)


    def get_context_data(self, **kwargs):
        context = super(SearchResultsView, self).get_context_data(**kwargs)
        return context


    def get_histogram(self, request):
        """ Function to create and save histogram of Hashtag.locations """
        # create the histogram
        plt.show()
        img_in_memory = BytesIO()
        plt.savefig(img_in_memory, format="png")
        image = base64.b64encode(img_in_memory.getvalue())
        context = {'image':image}
        return context

Results.html

<img src="data:image/png;base64,{{image}}" alt="Location Histogram" />

SOLUTION

In addition to issues with get and get_context_data as outlined by @ruddra below, another issue was that I had to decode the base64 string as a Unicode string. For more information, see here.

To do so, I included: image = image.decode('utf8')

So that, views.py looks like this:

def get_histogram(self, request):
    # draw histogram
    plt.show()
    img_in_memory = BytesIO()
    plt.savefig(img_in_memory, format="png") # save the image in memory using BytesIO
    img_in_memory.seek(0) # rewind to beginning of file
    image = base64.b64encode(img_in_memory.getvalue()) # load the bytes in the context as base64
    image = image.decode('utf8')
    return {'image':image}

回答1:

You are calling the get_histogram in wrong way. You can do it like this:

class SearchResultsView(DetailsView):
    ...

    def get_context_data(self, **kwargs):
         context = super(SearchResultsView, self).get_context_data(**kwargs)
         context.update(self.get_histogram(self.request))
         return context

You don't need to call the get_histogram method in get, or override the get method.

Update

I have tried like this:

 class SearchResultsView(DetailsView):
     ...

     def get_histogram(self):
         x = 2
         y = 3
         z = 2
         t= 3    
         plt.plot(x, y)
         plt.plot(z, t)
         plt.show()
         img_in_memory = io.BytesIO()  # for Python 3
         plt.savefig(img_in_memory, format="png")
         image = base64.b64encode(img_in_memory.getvalue())
         return {'image':image}

     def get_context_data(self, *args, **kwargs):
         context = super(SearchResultsView, self).get_context_data(*args, **kwargs)
         context.update(self.get_histogram())
         return context

Output looks like this:

来源：https://stackoverflow.com/questions/53127869/how-to-create-an-bytesio-img-and-pass-to-template

标签

django