<!--index.wxml-->
<view class="container">
 <input type="text" class="input" bindinput='input'/>
 <button bindtap="calculate">cal</button>
 <view>{{ result }}</view>
</view>

/**index.wxss**/
.input {
 border: 1px solid black;
 margin-bottom: 5px;
}

//index.js
//获取应用实例
const app = getApp()

Page({
 data: {
  result: "暂无结果",
  formula: ''
 },
 //事件处理函数
 calculate: function () {
  wx.request({
   url: 'https://shatter.xin/calculate',
   data: {
    formula: this.data.formula
   },
   success: res => {
    if (res.statusCode == 200) {
     this.setData({
      result: res.data
     })
    }
   }
  })
 },
 input: function (e) {
  this.setData({
   formula: e.detail.value
  })
 }
})

pip3 install django

django-admin startproject calculator
cd calculator

cd calculator
python3 manage.py runserver 0.0.0.0:8000

python3 manage.py startapp CalculateApi

INSTALLED_APPS = [
  'django.contrib.admin',
  'django.contrib.auth',
  'django.contrib.contenttypes',
  'django.contrib.sessions',
  'django.contrib.messages',
  'django.contrib.staticfiles',
  'CalculateApi'
]

from django.contrib import admin
from django.urls import path
from django.conf.urls import url, include

urlpatterns = [
  path('admin/', admin.site.urls),
  url('^', include('CalculateApi.urls')),
]

from django.conf.urls import url
from . import views

urlpatterns = [
  url('calculate', views.calculate)
]

from django.http import HttpResponse


def calculate(request):
  formula = request.GET['formula']
  try:
    result = eval(formula, {})
  except:
    result = 'Error formula'
  return HttpResponse(result)