jinja2 sample code

data.txt

{
  "greeting": "おはようございます",
  "name": "先生"
}

main.py

from jinja2 import Template
import json

def loadFile(filePath):
  with open(filePath, 'r', encoding='utf-8') as f:
    return f.read()

def loadTemplate(filePath):
  templateString = loadFile(filePath)
  return Template(templateString)

def loadData(filePath):
  dataString = loadFile(filePath)
  return json.loads(dataString)

template = loadTemplate('template.txt');
data = loadData('data.txt')
output = template.render(data)

print(output)

template.py

{{greeting}}, {{name}}