In the example in the referenced docs, there are two places where an instance of the form is created. What are those two lines? Follow up question, what is the line in your code where you are creating the form? Follow up question #2, what is the difference between the examples in the docs and your code?
I myself found the solution to this question:
I have written the format of rendering the context in my view wrongly, it is supposed to be: context ={"form":form}
All set!