DZone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
Refcards Trend Reports Events Over 2 million developers have joined DZone. Join Today! Thanks for visiting DZone today,
Edit Profile Manage Email Subscriptions Moderation Admin Console How to Post to DZone Article Submission Guidelines
View Profile
Sign Out
Refcards
Trend Reports
Events
Zones
Culture and Methodologies Agile Career Development Methodologies Team Management
Data Engineering AI/ML Big Data Data Databases IoT
Software Design and Architecture Cloud Architecture Containers Integration Microservices Performance Security
Coding Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
Culture and Methodologies
Agile Career Development Methodologies Team Management
Data Engineering
AI/ML Big Data Data Databases IoT
Software Design and Architecture
Cloud Architecture Containers Integration Microservices Performance Security
Coding
Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance
Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
  1. DZone
  2. Coding
  3. Languages
  4. Dealing With a TypeError in Python 3

Dealing With a TypeError in Python 3

When I finally upgraded to Python 3, I realized that one of my scripts that writes JSON to a file no longer works. Read on to find out how I resolved it.

Mark Needham user avatar by
Mark Needham
·
Apr. 12, 17 · Tutorial
Like (0)
Save
Tweet
Share
7.31K Views

Join the DZone community and get the full member experience.

Join For Free

I recently upgraded to Python 3 (I know, took me a while!) and realized that one of my scripts that writes JSON to a file no longer works!

This is a simplified version of what I’m doing:

>>> import json
>>> x = {"mark": {"name": "Mark"}, "michael": {"name": "Michael"}  } 
>>> json.dumps(x.values())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 180, in default
    o.__class__.__name__)
TypeError: Object of type 'dict_values' is not JSON serializable

Python 2.7 would be perfectly happy:

>>> json.dumps(x.values())
'[{"name": "Michael"}, {"name": "Mark"}]'

The difference is in the results returned by the values method:

# Python 2.7.10
>>> x.values()
[{'name': 'Michael'}, {'name': 'Mark'}]

# Python 3.6.0
>>> x.values()
dict_values([{'name': 'Mark'}, {'name': 'Michael'}])
>>>

Python 3 no longer returns an array. Instead, we have a dict_values wrapper around the data.

Luckily this is easy to resolve; we just need to wrap the call to values with a call to list:

>>> json.dumps(list(x.values()))
'[{"name": "Mark"}, {"name": "Michael"}]'

This versions works with Python 2.7, as well, so if I accidentally run the script with an old version, the world isn’t going to explode!

Python (language)

Published at DZone with permission of Mark Needham, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

Popular on DZone

  • The Data Leakage Nightmare in AI
  • Tech Layoffs [Comic]
  • Kotlin Is More Fun Than Java And This Is a Big Deal
  • Implementing Infinite Scroll in jOOQ

Comments

Partner Resources

X

ABOUT US

  • About DZone
  • Send feedback
  • Careers
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • Become a Contributor
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 600 Park Offices Drive
  • Suite 300
  • Durham, NC 27709
  • support@dzone.com
  • +1 (919) 678-0300

Let's be friends: