what is queryset in django

1import pandas as pd
2import datetime
3from myapp.models import BlogPost
4
5df = pd.DataFrame(list(BlogPost.objects.all().values()))
6df = pd.DataFrame(list(BlogPost.objects.filter(date__gte=datetime.datetime(2012, 5, 1)).values()))
7
8# limit which fields
9df = pd.DataFrame(list(BlogPost.objects.all().values('author', 'date', 'slug')))

1A QuerySet is a list of a dictionary of objects in your database.

1what is queryset in django?
2
3A QuerySet represents a collection of objects from your database. 
4It can have zero, one or many filters. 
5Filters narrow down the query results based on the given parameters. 
6In SQL terms, a QuerySet equates to a SELECT statement, and a filter is a limiting clause such as WHERE or LIMIT.

1They indeed do different things.
2
3get()
4This is a top-level method, and there's one for each HTTP verb - get(), post(), patch(), etc. You would override it when you want to do something before a request is processed by the view, or after. But this is only called when a form view is loaded for the first time, not when the form is submitted. Basic example in the documentation. By default it will just render the configured template and return the HTML.
5
6class MyView(TemplateView):
7    # ... other methods
8
9    def get(self, *args, **kwargs):
10        print('Processing GET request')
11        resp = super().get(*args, **kwargs)
12        print('Finished processing GET request')
13        return resp
14get_queryset()
15Used by ListViews - it determines the list of objects that you want to display. By default, it will just give you all for the model you specify. By overriding this method you can extend or completely replace this logic. Django documentation on the subject.
16
17class FilteredAuthorView(ListView):
18    template_name = 'authors.html'
19    model = Author
20
21    def get_queryset(self):
22        # original qs
23        qs = super().get_queryset() 
24        # filter by a variable captured from url, for example
25        return qs.filter(name__startswith=self.kwargs['name'])
26get_context_data()
27This method is used to populate a dictionary to use as the template context. For example, ListViews will populate the result from get_queryset() as author_list in the above example. You will probably be overriding this method most often to add things to display in your templates.
28
29def get_context_data(self, **kwargs):
30    data = super().get_context_data(**kwargs)
31    data['page_title'] = 'Authors'
32    return data
33And then in your template, you can reference these variables.
34
35<h1>{{ page_title }}</h1>
36
37<ul>
38{% for author in author_list %}
39    <li>{{ author.name }}</li>
40{% endfor %}
41</ul>
42Now to answer your main question, the reason you have so many methods is to let you easily stick your custom logic with pin-point accuracy. It not only allows your code to be more readable and modular, but also more testable.
43
44The documentation should explain everything. If still not enough, you may find the sources helpful as well. You'll see how everything is implemented with mixins which are only possible because everything is compartmentalized.

1# Get blogs entries with id 1, 4 and 7
2>>> Blog.objects.filter(pk__in=[1,4,7])
3
4# Get all blog entries with id > 14
5>>> Blog.objects.filter(pk__gt=14)
6