The script for switching two WebViews on Pythonista 3.

translate_set.py

import ui
import console
import sys


user_action = True


class MyWebViewDelegate(object):
    def webview_should_start_load(self, webview, url, nav_type):
        global user_action
        if nav_type == 'link_clicked' or user_action:
            textfield = webview.superview['textfield1']
            textfield.text = url
            user_action = False
        return True

    def webview_did_start_load(self, webview):
        pass

    def webview_did_finish_load(self, webview):
        pass

    def webview_did_fail_load(self, webview, error_code, error_msg):
        pass


def page_back(sender):
    global user_action
    user_action = True
    webview = sender.superview['webview1']
    webview.go_back()

def page_forward(sender):
    global user_action
    user_action = True
    webview = sender.superview['webview1']
    webview.go_forward()

def jump_to_link(sender):
    global user_action
    user_action = True
    textfield = sender.superview['textfield1']
    if textfield.text:
        webview = sender.superview['webview1']
        webview.load_url(textfield.text)

def switch_webview(sender):
    idx = sender.selected_index
    webview1 = sender.superview['webview1']
    webview2 = sender.superview['webview2']
    if idx == 0:
        webview2.alpha = 0.0
        webview1.alpha = 1.0
        webview1.bring_to_front()
    else:
        webview1.alpha = 0.0
        webview2.alpha = 1.0
        webview2.bring_to_front()

v = ui.load_view('translate_set')

textfield = v['textfield1']
textfield.clear_button_mode = 'unless_editing'

webview1 = v['webview1']
webview1.delegate = MyWebViewDelegate()
text = ''
if len(sys.argv) > 1:
    text = sys.argv[1]
if text.startswith('http://') or text.startswith('https://'):
    result = console.alert('URLを開く', '取得済みのURLがあります。開きますか？', 'はい', 'Googleを開く', 'Pythonista Docs を開く')
    if result == 2:
        webview1.load_url('https://www.google.co.jp/')
        textfield.text = 'https://www.google.co.jp/'
    elif result == 3:
        webview1.load_url('http://omz-software.com/pythonista/docs/')
        textfield.text = 'http://omz-software.com/pythonista/docs/'
    else:
        webview1.load_url(text)
        textfield.text = text
else:
    result = console.alert('URLを選択', 'どちらを開きますか？', 'Googleを開く', 'Pythonista Docs を開く')
    if result == 1:
        webview1.load_url('https://www.google.co.jp/')
        textfield.text = 'https://www.google.co.jp/'
    else:
        webview1.load_url('http://omz-software.com/pythonista/docs/')
        textfield.text = 'http://omz-software.com/pythonista/docs/'

webview2 = v['webview2']
webview2.load_url('https://translate.google.co.jp/?hl=ja&tab=wT')
webview2.alpha = 0.0

webview1.bring_to_front()

v.present('sheet')

translate_set.pyui

[
  {
    "nodes" : [
      {
        "nodes" : [

        ],
        "frame" : "{{6, 6}, {151, 32}}",
        "class" : "TextField",
        "attributes" : {
          "uuid" : "97EF78A8-7CC4-4E0B-B95D-934CEB909B49",
          "flex" : "W",
          "frame" : "{{20, 104}, {200, 32}}",
          "border_color" : "RGBA(0.593750,0.825893,1.000000,1.000000)",
          "alignment" : "left",
          "autocorrection_type" : "default",
          "placeholder" : "input some URL",
          "font_name" : "<System>",
          "spellchecking_type" : "default",
          "class" : "TextField",
          "name" : "textfield1",
          "font_size" : 17
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{165, 6}, {32, 32}}",
        "class" : "Button",
        "attributes" : {
          "flex" : "L",
          "action" : "jump_to_link",
          "font_size" : 15,
          "frame" : "{{80, 104}, {80, 32}}",
          "title" : "",
          "uuid" : "41B10096-4A2B-406B-B7CE-9EF4CA0FA54D",
          "class" : "Button",
          "name" : "button1",
          "image_name" : "iob:ios7_search_strong_32"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{198, 6}, {32, 32}}",
        "class" : "Button",
        "attributes" : {
          "flex" : "L",
          "action" : "page_back",
          "font_size" : 15,
          "frame" : "{{80, 104}, {80, 32}}",
          "title" : "",
          "uuid" : "E73EF2B7-D590-45AA-B26B-F0C51577F19F",
          "class" : "Button",
          "name" : "button2",
          "image_name" : "iob:ios7_arrow_left_32"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{231, 6}, {32, 32}}",
        "class" : "Button",
        "attributes" : {
          "flex" : "L",
          "action" : "page_forward",
          "font_size" : 15,
          "frame" : "{{80, 104}, {80, 32}}",
          "title" : "",
          "uuid" : "E44E9F06-9F00-45B7-B286-9DA6285A21E9",
          "class" : "Button",
          "name" : "button3",
          "image_name" : "iob:ios7_arrow_right_32"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{0, 77}, {263, 263}}",
        "class" : "WebView",
        "attributes" : {
          "scales_to_fit" : true,
          "frame" : "{{20, 20}, {200, 200}}",
          "flex" : "WH",
          "class" : "WebView",
          "name" : "webview1",
          "uuid" : "E3DAFEDA-C701-49DC-9344-038DA741FEE9"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{46, 43}, {172, 29}}",
        "class" : "SegmentedControl",
        "attributes" : {
          "action" : "switch_webview",
          "flex" : "LR",
          "segments" : "サイトビュー|Google翻訳",
          "frame" : "{{68, 280}, {120, 29}}",
          "class" : "SegmentedControl",
          "uuid" : "3FA1B71E-C34E-46B0-8EFD-236DFF7F774C",
          "name" : "segmentedcontrol1"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{0, 77}, {263, 263}}",
        "class" : "WebView",
        "attributes" : {
          "uuid" : "92B073BF-5420-4248-AA00-45613A67ED82",
          "frame" : "{{28, 194}, {200, 200}}",
          "scales_to_fit" : true,
          "class" : "WebView",
          "name" : "webview2",
          "flex" : "WH"
        },
        "selected" : false
      }
    ],
    "frame" : "{{0, 0}, {263, 340}}",
    "class" : "View",
    "attributes" : {
      "background_color" : "RGBA(1.000000,1.000000,1.000000,1.000000)",
      "enabled" : true,
      "tint_color" : "RGBA(0.000000,0.478000,1.000000,1.000000)",
      "name" : "Google翻訳切替ビューア",
      "border_color" : "RGBA(0.000000,0.000000,0.000000,1.000000)",
      "flex" : ""
    },
    "selected" : false
  }
]