Manually create files from rendering odoo qweb

Question

Question: How can I create in python a pdf file using qweb, like Jinja with render_template(template, context)?

Problem explained:

Hello, I'm new to Odoo.
I have to create a wizard which create a folder with different reports, and make it accessible in the following download view.

Folder structure to zip and download:

expenses_report
├── EMPLOYEE1_04-56,8
│   ├── expenses_report_EMPLOYEE1_04_56,8.pdf
│   ├── internet_bill.pdf
│   ├── meal_justificative.pdf
│   └── transport_bill.pdf
└── EMPLOYEE2_04-25,6
    ├── another_justificative.jpg
    └── expenses_report_EMPLOYEE2_04_25,6.pdf

As you can see, I have to do a bit of python, but that's not the problem.
For the expenses_report, I have to take the qweb report linked to the "Print" button on expenses view, BUT I have to put many expenses that where query-ed in python on wizard click.

So, you can now read again the question

PS: my pseudo code:

@api.multi
def export_new_expenses(self):
    attachments_by_employee = self._get_new_attachments()
    self._copy_attachments_in_tmp_folder(attachments_by_employee)
    self._create_expense_reports(attachments_by_employee)
    file_record = self._create_zip_file_record()
    return self._download_view(file_record)