Good old-fashioned phone calls remain one of the best forms of communication despite the slew of new smartphone apps that have popped up over the past several years. With just a few lines of Python code plus a web application programming interface we can make and receive phone calls from any application.

Our example calls will say a snippet of text and put all incoming callers into a recorded conference call. You can modify the instructions using Twilio's TwiML verbs when you perform different actions in your own application's phone calls.

Our Tools

You should have either Python 2 or 3 installed to build this application. Throughout the post we will also use:

• pip and virtualenv to handle application dependencies
• A free Twilio account to use their phone calling web API
• Twilio's Python helper library, version 5.7.0, which is available on PyPI

You can snag all the open source code for this tutorial in the python-twilio-example-apps GitHub repository under the no-framework/phone-calls directory. Use and copy the code for your own applications. Everything in that repository and in this blog post are open source under the MIT license.

Install App Dependencies

Our application will use the TwilioPython helper library to create an HTTP POST request to Twilio's API. The Twilio helper library is installable from PyPI into a virtual environment. Open your terminal and use the virtualenv command to create a new virtualenv:

virtualenv phoneapp

Invoke the activate script within the virtualenv bin/ directory to make this virtualenv the active Python executable. Note that you will need to perform this step in every terminal window that you want the virtualenv to be active.

source phoneapp/bin/activate

The command prompt will change after activating the virtualenv to something like (phoneapp) $.

Next use the pip command to install the Twilio Python package into the virtualenv.

pip install twilio==5.7.0

We will have the required dependency ready for project as soon as the installation script finishes. Now we can write and execute Python code to dial phone numbers.

Our Python Script

Create a new file named phone_calls.py and copy or type in the following lines of code.

fromtwilio.restimportTwilioRestClient# Twilio phone number goes here. Grab one at https://twilio.com/try-twilio# and use the E.164 format, for example: "+12025551234"TWILIO_PHONE_NUMBER=""# list of one or more phone numbers to dial, in "+19732644210" formatDIAL_NUMBERS=["",]# URL location of TwiML instructions for how to handle the phone callTWIML_INSTRUCTIONS_URL= \
  "http://static.fullstackpython.com/phone-calls-python.xml"# replace the placeholder values with your Account SID and Auth Token# found on the Twilio Console: https://www.twilio.com/consoleclient=TwilioRestClient("ACxxxxxxxxxx","yyyyyyyyyy")defdial_numbers(numbers_list):"""Dials one or more phone numbers from a Twilio phone number."""fornumberinnumbers_list:print("Dialing "+number)# set the method to "GET" from default POST because Amazon S3 only# serves GET requests on files. Typically POST would be used for appsclient.calls.create(to=number,from_=TWILIO_PHONE_NUMBER,url=TWIML_INSTRUCTIONS_URL,method="GET")if__name__=="__main__":dial_numbers(DIAL_NUMBERS)

There are a few lines that you need to modify in this application before it will run. First, insert one or more phone numbers you wish to dial into the DIAL_NUMBERS list. Each one should be a string, separated by a comma. For example, DIAL_NUMBERS = ["+12025551234", "+14155559876", "+19735551234"].

Next, TWILIO_PHONE_NUMBER and the Account SID and Authentication Token, found on the client = TwilioRestClient("ACxxxxxxxxxx", "yyyyyyyyyy") line, need to be set. We can get these values from the Twilio Console.

In your web browser go to the Twilio website and sign up for a free account or sign into your existing Twilio account.

Copy the Account SID and Auth Token from the Twilio Console and paste them into your application's code:

The Twilio trial account allows you to dial and receive phone calls to your own validated phone number. To handle calls from any phone number then you need to upgrade your account (hit the upgrade button on the top navigation bar).

Once you are signed into your Twilio account, go to the manage phone numbers screen. On this screen you can buy one or more phone numbers or click on an existing phone number in your account to configure it.

After clicking on a number you will reach the phone number configuration screen. Paste in the URL with TwiML instructions and change the dropdown from "HTTP POST" to "HTTP GET". In this post we'll use http://static.fullstackpython.com/phone-calls-python.xml, but that URL can be more than just a static XML file.

The power of Twilio really comes in when that URL is handled by your web application so it can dynamically respond with TwiML instructions based on the incoming caller number or other properties stored in your database.

Under the Voice webhook, paste in http://static.fullstackpython.com/phone-calls-python.xml and change the drop-down to the right from "HTTP POST" to "HTTP GET". Click the "Save" button at the bottom of the screen.

Now try calling your phone number. You should hear the snippet of text read by the Alice voice and then you will be placed into a conference call. If no one else calls the number then hold music should be playing.

Making Phone Calls

We just handled inbound phone calls to our phone number. Now it's time to dial outbound phone calls. Make sure your phone_calls.py file is saved and that your virtualenv is still activated and then execute the script:

python phone_calls.py

In a moment all the phone numbers you write in the DIAL_NUMBERS list should light up with calls. Anyone that answers will hear our message read by the "Alice" voice and then they'll be placed together into a recorded conference call, just like when someone dials into the number.

Here is my inbound phone call:

Not bad for just a few lines of Python code!

Next Steps

Now that we know how to make and receive phone calls from a Twilio number that follows programmatic instructions we can do a whole lot more in our applications. Next you can use one of these tutorials to do more with your phone number:

• Build a phone-calling Slack bot
• Mask phone numbers for anonymous communication
• Add call tracking to see metrics for phone calls

Questions? Contact me via Twitter @fullstackpython or @mattmakai. I'm also on GitHub as mattmakai.

See something wrong in this post? Fork this page's source on GitHub and submit a pull request.

C:\Python27>cd Scripts

C:\Python27\Scripts>pip install pyquery
Collecting pyquery
  Downloading pyquery-1.2.17-py2.py3-none-any.whl
Requirement already satisfied: lxml>=2.1 in c:\python27\lib\site-packages (from pyquery)
Requirement already satisfied: cssselect>0.7.9 in c:\python27\lib\site-packages (from pyquery)
Installing collected packages: pyquery
Successfully installed pyquery-1.2.17

from pyquery import PyQuery

seeds = [
    'https://twitter.com',
    'http://google.com'
]

crawl_frontiers = []

def start_crawler():
    crawl_frontiers = crawler_seeds()

    print(crawl_frontiers)

def crawler_seeds():
    frontiers = []
    for index, seed in enumerate(seeds):
        frontier = {index: read_links(seed)}
        frontiers.append(frontier)

    return frontiers

def read_links(seed):
    crawler = PyQuery(seed)
    return [crawler(tag_a).attr("href") for tag_a in crawler("a")]

start_crawler()

Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:42:59) [MSC v.1500 32 bit (Intel)] on win32

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtGui

"""
Qt.Gui calculator example
"""

class Example(QtGui.QWidget):

    def __init__(self):
        super(Example, self).__init__()

        self.initUI()

    def initUI(self):
 title = QtGui.QLabel('Title')
        titleEdit = QtGui.QLineEdit()
        grid = QtGui.QGridLayout()
 grid.setSpacing(10)

 grid.addWidget(title, 0, 0)

 grid.addWidget(titleEdit,0,1,1,4)

        self.setLayout(grid)

        names = ['Cls', 'Bck', 'OFF',
                 '/', '.', '7', '8',
                '9', '*', 'SQR', '3',
                 '4', '5', '-', '=',
                '0', '1', '2', '+']

        positions = [(i,j) for i in range(1,5) for j in range(0,5)]

        for position, name in zip(positions, names):

            if name == '':
                continue
            button = QtGui.QPushButton(name)
            grid.addWidget(button, *position)

        self.move(300, 250)
        self.setWindowTitle('Calculator')
        self.show()

def main():
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

C:\Python27>cd Scripts

C:\Python27\Scripts>pip install pyinstaller
Collecting pyinstaller
  Downloading PyInstaller-3.2.1.tar.bz2 (2.4MB)
    100% |################################| 2.4MB 453kB/s
....
Collecting pypiwin32 (from pyinstaller)
  Downloading pypiwin32-219-cp27-none-win32.whl (6.7MB)
    100% |################################| 6.7MB 175kB/s
...
Successfully installed pyinstaller-3.2.1 pypiwin32-219

from tkinter import Tk, Label, Button

class MyFirstGUI:
    def __init__(self, master):
        self.master = master
        master.title("A simple GUI")

        self.label = Label(master, text="This is our first GUI!")
        self.label.pack()

        self.greet_button = Button(master, text="Greet", command=self.greet)
        self.greet_button.pack()

        self.close_button = Button(master, text="Close", command=master.quit)
        self.close_button.pack()

    def greet(self):
        print("Greetings!")

root = Tk()
my_gui = MyFirstGUI(root)
root.mainloop()

C:\Python27\Scripts>pyinstaller.exe   --onefile --windowed ..\tk_app.py
92 INFO: PyInstaller: 3.2.1
92 INFO: Python: 2.7.13
93 INFO: Platform: Windows-10-10.0.14393
93 INFO: wrote C:\Python27\Scripts\tk_app.spec
95 INFO: UPX is not available.
96 INFO: Extending PYTHONPATH with paths
['C:\\Python27', 'C:\\Python27\\Scripts']
96 INFO: checking Analysis
135 INFO: checking PYZ
151 INFO: checking PKG
151 INFO: Building because toc changed
151 INFO: Building PKG (CArchive) out00-PKG.pkg
213 INFO: Redirecting Microsoft.VC90.CRT version (9, 0, 21022, 8) -> (9, 0, 30729, 9247)
2120 INFO: Building PKG (CArchive) out00-PKG.pkg completed successfully.
2251 INFO: Bootloader c:\python27\lib\site-packages\PyInstaller\bootloader\Windows-32bit\runw.exe
2251 INFO: checking EXE
2251 INFO: Rebuilding out00-EXE.toc because tk_app.exe missing
2251 INFO: Building EXE from out00-EXE.toc
2267 INFO: Appending archive to EXE C:\Python27\Scripts\dist\tk_app.exe
2267 INFO: Building EXE from out00-EXE.toc completed successfully.

C:\Python27\Scripts>C:\Python27\Scripts\dist\tk_app.exe

C:\Python27\Scripts>

# UTF-8
#
# For more details about fixed file info 'ffi' see:
# http://msdn.microsoft.com/en-us/library/ms646997.aspx
VSVersionInfo(
  ffi=FixedFileInfo(
    # filevers and prodvers should be always a tuple with four items: (1, 2, 3, 4)
    # Set not needed items to zero 0.
    filevers=(2017, 1, 1, 1),
    prodvers=(1, 1, 1, 1),
    # Contains a bitmask that specifies the valid bits 'flags'
    mask=0x3f,
    # Contains a bitmask that specifies the Boolean attributes of the file.
    flags=0x0,
    # The operating system for which this file was designed.
    # 0x4 - NT and there is no need to change it.
    OS=0x4,
    # The general type of file.
    # 0x1 - the file is an application.
    fileType=0x1,
    # The function of the file.
    # 0x0 - the function is not defined for this fileType
    subtype=0x0,
    # Creation date and time stamp.
    date=(0, 0)
    ),
  kids=[
    StringFileInfo(
      [
      StringTable(
        u'040904b0',
        [StringStruct(u'CompanyName', u'python-catalin'),
        StringStruct(u'ProductName', u'test'),
        StringStruct(u'ProductVersion', u'1, 1, 1, 1'),
        StringStruct(u'InternalName', u'tk_app'),
        StringStruct(u'OriginalFilename', u'tk_app.exe'),
        StringStruct(u'FileVersion', u'2017, 1, 1, 1'),
        StringStruct(u'FileDescription', u'test tk'),
        StringStruct(u'LegalCopyright', u'Copyright 2017 free-tutorials.org.'),
        StringStruct(u'LegalTrademarks', u'tk_app is a registered trademark of catafest.'),])
      ]),
    VarFileInfo([VarStruct(u'Translation', [0x409, 1200])])
  ]
)

 pyinstaller.exe --onefile --windowed --version-file=..\version.txt ..\tk_app.py

• Fast! Translate an entire book in less than 5 seconds.
• Made for Python 3 but still works on Python 2
• Fast and easy to install, easy to use
• Supports translation from any language
• Highly composable interface, the power of Unix pipes and filters.
• Simple API and documentation

C:\>cd Python27

C:\Python27>cd Scripts

C:\Python27\Scripts>pip install py-translate
Collecting py-translate
  Downloading py_translate-1.0.3-py2.py3-none-any.whl (61kB)
    100% |################################| 61kB 376kB/s
Installing collected packages: py-translate
Successfully installed py-translate-1.0.3

C:\Python27\Scripts>

>>> import translate
>>> dir(translate)
['TestLanguages', 'TestTranslator', '__author__', '__build__', '__builtins__', '__copyright__', '__doc__', '__file__', '__license__', '__name__', '__package__', '__path__', '__title__', '__version__', 'accumulator', 'coroutine', 'coroutines', 'languages', 'print_table', 'push_url', 'set_task', 'source', 'spool', 'tests', 'translation_table', 'translator', 'write_stream']
>>> from translate import translator
>>> translator('ro', 'en', 'Consider ca dezvoltarea personala este un pas important')
[[[u'I think personal development is an important step', u'Consider ca dezvoltarea personala este un pas important', None, None, 0]], None, u'ro']
>>>

1. What's the efficiency difference between using "+" and "," in print()? - [14/7]
2. Unexpected result from `in` operator - Python - [13/3]
3. Why is deque implemented as a linked list instead of a circular array? - [13/2]
4. What is co_names? - [10/1]
5. list comprehension in exec with empty locals: NameError - [9/4]
6. Add values of keys and sort it by occurrence of the keys in a list of dictionaries in Python - [8/5]
7. Pandas - return n smallest indexes by column - [8/3]
8. Differences between generator comprehension expressions - [8/1]
9. Sort 2 lists in Python based on the ratio of individual corresponding elements or based on a third list - [7/4]
10. Dynamically generating elements of list within list - [7/3]

How do you know whether your application is running properly with minimal errors after building and deploying it? The fastest and easiest way to monitor your operational Flask web application is to integrate one of the many available fantastic hosted monitoring tools.

In this post we will quickly add Rollbar monitoring to catch errors and visualize our application is running properly. There are also many other great hosted monitoring tools, which you can check out on the monitoring page.

Our Tools

We can use either Python 2 or 3 to build this tutorial, but Python 3 is strongly recommended for all new applications. I used Python 3.6.2 to execute my code. We will also use the following application dependencies throughout the post:

• Flask web framework, version 0.12.2
• pyrollbar monitoring instrumentation library, version 0.13.12
• blinker for signaling support in Flask applications so pyrollbar can report on all errors
• A free Rollbar account where we will send error data and view it when it is captured
• pip and the virtualenv virtual environment library, which come packaged with Python 3, to install and isolate the Flask and Rollbar libraries from other Python projects you are working on

If you need help getting your development environment configured before running this code, take a look at this guide for setting up Python 3 and Flask on Ubuntu 16.04 LTS.

All code in this blog post is available open source under the MIT license on GitHub under the monitor-flask-apps directory of the blog-code-examples repository. Use and abuse the source code as you desire for your own applications.

Installing Dependencies

Change into the directory where you keep your Python virtualenvs. Create a new virtual environment for this project using the following command.

python3 -m venv monitorflask

Activate the virtualenv.

source monitorflask/bin/activate

The command prompt will change after activating the virtualenv:

Remember that you need to activate the virtualenv in every new terminal window where you want to use the virtualenv to run the project.

Flask, Rollbar and Blinker can now be installed into the now-activated virtualenv.

pip install flask==0.12.2 rollbar==0.13.12 blinker==1.4

Our required dependencies should be installed within our virtualenv after a short installation period. Look for output like the following to confirm everything worked.

Installing collected packages: blinker, itsdangerous, click, MarkupSafe, Jinja2, Werkzeug, Flask, idna, urllib3, chardet, certifi, requests, six, rollbar
  Running setup.py install for blinker ... done
  Running setup.py install for itsdangerous ... done
  Running setup.py install for MarkupSafe ... done
  Running setup.py install for rollbar ... done
Successfully installed Flask-0.12.2 Jinja2-2.9.6 MarkupSafe-1.0 Werkzeug-0.12.2 blinker-1.4 certifi-2017.4.17 chardet-3.0.4 click-6.7 idna-2.5 itsdangerous-0.24 requests-2.18.1 rollbar-0.13.12 six-1.10.0 urllib3-1.21.1

Now that we have our Python dependencies installed into our virtualenv we can create the initial version of our application.

Building Our Flask App

Create a folder for your project named monitor-flask-apps. Change into the folder and then create a file named app.py with the following code.

importrefromflaskimportFlask,render_template,Responsefromwerkzeug.exceptionsimportNotFoundapp=Flask(__name__)MIN_PAGE_NAME_LENGTH=2@app.route("/<string:page>/")defshow_page(page):try:valid_length=len(page)>=MIN_PAGE_NAME_LENGTHvalid_name=re.match('^[a-z]+$',page.lower())isnotNoneifvalid_lengthandvalid_name:returnrender_template("{}.html".format(page))else:msg="Sorry, couldn't find page with name {}".format(page)raiseNotFound(msg)except:returnResponse("404 Not Found")if__name__=="__main__":app.run(debug=True)

The above application code has some standard Flask imports so we can create a Flask web app and render template files. We have a single function named show_page to serve a single Flask route. show_page checks if the URL path contains only lowercase alpha characters for a potential page name. If the page name can be found in the templates folder then the page is rendered, otherwise an exception is thrown that the page could not be found. We need to create at least one template file if our function is ever going to return a non-error reponse.

Save app.py and make a new subdirectory named templates under your project directory. Create a new file named battlegrounds.html and put the following Jinja2 template markup into it.

<!DOCTYPE html><html><head><title>You found the Battlegrounds GIF!</title></head><body><h1>PUBG so good.</h1><imgsrc="https://media.giphy.com/media/3ohzdLMlhId2rJuLUQ/giphy.gif"></body></html>

The above Jinja2 template is basic HTML without any embedded template tags. The template creates a very plain page with a header description of "PUBG so good" and a GIF from this excellent computer game.

Time to run and test our code. Change into the base directory of your project where app.py file is located. Execute app.py using the python command as follows (make sure your virtualenv is still activated in the terminal where you are running this command):

python app.py

The Flask development server should start up and display a few lines of output.

What happens when we access the application running on localhost port 5000?

HTTP status 404 page not found, which is what we expected because we only defined a single route and it did not live at the base path.

We created a template named battlegrounds.html that should be accessible when we go to localhost:5000/battlegrounds/.

The application successfully found the battlegrounds.html template but that is the only one available. What if we try localhost:5000/fullstackpython/?

HTTP 500 error. That's no good.

The 404 and 500 errors are obvious to us right now because we are testing the application locally. However, what happens when the app is deployed and a user gets the error in their own web browser? They will typically quit out of frustration and you will never know what happened unless you add some error tracking and application monitoring.

We will now modify our code to add Rollbar to catch and report those errors that occur for our users.

Handling Errors

Head to Rollbar's homepage so we can add their hosted monitoring tools to our oft-erroring Flask app.

Click the "Sign Up" button in the upper right-hand corner. Enter your email address, a username and the password you want on the sign up page.

After the sign up page you will see the onboarding flow where you can enter a project name and select a programming language. For project name enter "Battlegrounds" and select that you are monitoring a Python app.

Press the "Continue" button at the bottom to move along. The next screen shows us a few quick instructions to add monitoring to our Flask application.

Let's modify our Flask application to test whether we can properly connect to Rollbar's service. Change app.py to include the following highlighted lines.

~~importosimportre~~importrollbarfromflaskimportFlask,render_template,Responsefromwerkzeug.exceptionsimportNotFoundapp=Flask(__name__)MIN_PAGE_NAME_LENGTH=2~~@app.before_first_request~~defadd_monitoring():~~rollbar.init(os.environ.get('ROLLBAR_SECRET'))~~rollbar.report_message('Rollbar is configured correctly')@app.route("/<string:page>/")defshow_page(page):try:valid_length=len(page)>=MIN_PAGE_NAME_LENGTHvalid_name=re.match('^[a-z]+$',page.lower())isnotNoneifvalid_lengthandvalid_name:returnrender_template("{}.html".format(page))else:msg="Sorry, couldn't find page with name {}".format(page)raiseNotFound(msg)except:returnResponse("404 Not Found")if__name__=="__main__":app.run(debug=True)

We added a couple of new imports, os and rollbar. os allows us to grab environment variable values, such as our Rollbar secret key. rollbar is the library we installed earlier. The two lines below the Flask app instantiation are to initialize Rollbar using the Rollbar secret token and send a message to the service that it started correctly.

The ROLLBAR_SECRET token needs to be set in an environment variable. Save an quit the app.py. Run export ROLLBAR_SECRET='token here' on the command line where your virtualenv is activated. This token can be found on the Rollbar onboarding screen.

I typically store all my environment variables in a file like template.env and invoke it from the terminal using the . ./template.env command. Make sure to avoid committing your secret tokens to a source control repository, especially if the repository is public!

After exporting your ROLLBAR_SECRET key as an environment variable we can test that Rollbar is working as we run our application. Run it now using python:

python app.py

Back in your web browser press the "Done! Go to Dashboard" button. Don't worry about the "Report an Error" section code, we can get back to that in a moment.

If the event hasn't been reported yet we'll see a waiting screen like this one:

Once Flask starts up though, the first event will be populated on the dashboard.

Okay, our first test event has been populated, but we really want to see all the errors from our application, not a test event.

Testing Error Handling

How do we make sure real errors are reported rather than just a simple test event? We just need to add a few more lines of code to our app.

importosimportreimportrollbar~~importrollbar.contrib.flaskfromflaskimportFlask,render_template,Response~~fromflaskimportgot_request_exceptionfromwerkzeug.exceptionsimportNotFoundapp=Flask(__name__)MIN_PAGE_NAME_LENGTH=2@app.before_first_requestdefadd_monitoring():rollbar.init(os.environ.get('ROLLBAR_SECRET'))~~## delete the next line if you dont want this event anymorerollbar.report_message('Rollbar is configured correctly')~~got_request_exception.connect(rollbar.contrib.flask.report_exception,app)@app.route("/<string:page>/")defshow_page(page):try:valid_length=len(page)>=MIN_PAGE_NAME_LENGTHvalid_name=re.match('^[a-z]+$',page.lower())isnotNoneifvalid_lengthandvalid_name:returnrender_template("{}.html".format(page))else:msg="Sorry, couldn't find page with name {}".format(page)raiseNotFound(msg)except:~~rollbar.report_exc_info()returnResponse("404 Not Found")if__name__=="__main__":app.run(debug=True)

The above highlighted code modifies the application so it reports all Flask errors as well as our HTTP 404 not found issues that happen within the show_page function.

Make sure your Flask development server is running and try to go to localhost:5000/b/. You will receive an HTTP 404 exception and it will be reported to Rollbar. Next go to localhost:5000/fullstackpython/ and an HTTP 500 error will occur.

You should see an aggregation of errors as you test out these errors:

Woohoo, we finally have our Flask app reporting all errors that occur for any user back to the hosted Rollbar monitoring service!

What's Next?

We just learned how to catch and handle errors with Rollbar as a hosted monitoring platform in a simple Flask application. Next you will want to add monitoring to your more complicated web apps. You can also check out some of Rollbar's more advanced features such as:

• tracking and debugging deployment issues
• sorting and viewing errors by user
• setting up custom rules to group errors

There is a lot more to learn about web development and deployments so keep learning by reading up on Flask and other web frameworks such as Django, Pyramid and Sanic. You can also learn more about integrating Rollbar with Python applications via their Python documentation.

Questions? Let me know via a GitHub issue ticket on the Full Stack Python repository, on Twitter @fullstackpython or @mattmakai.

See something wrong in this blog post? Fork this page's source on GitHub and submit a pull request with a fix.

Creating strings of the form “a, b, c and d” from a list [‘a’, ‘b’, ‘c’, ‘d’] is a task I faced some time ago, as I needed to include such strings in some HTML documents. The “,” and the “and” are included according to the amount of elements. [‘a’, ‘b’] yields “a and b“, [‘a’] yields “a” for example. In a recent review to the code, I changed the method from using string concatenation:

if len(items) > 1:
    text = items[0]
    for item in items[1:-1]:
        text += ', ' + item
    text += ' and ' + items[-1]
else:
    text = items[0]

to the use of slicing of the items list, addition of the resulting sublists and str.join to include the punctuation:

first = items[:1]
middle = items[1:-1]
last = items[1:][-1:]
first_middle = [', '.join(first + middle)]
text = ' and '.join(first_middle + last)

The old method requires an additonal elif branch to work when items is an empty list; the new method returns an empty string if the items list is empty. I share this tip in case it is useful to someone else.