Dealing with data is essential for any Pythonista, but sometimes that data is just not very pretty. Computers don’t care about formatting, but without good formatting, humans may find something hard to read. The output isn’t pretty when you use print() on large dictionaries or long lists—it’s efficient, but not pretty.
The pprint module in Python is a utility module that you can use to print data structures in a readable, pretty way. It’s a part of the standard library that’s especially useful for debugging code dealing with API requests, large JSON files, and data in general.
By the end of this tutorial, you’ll:
- Understand why the
pprintmodule is necessary - Learn how to use
pprint(),PrettyPrinter, and their parameters - Be able to create your own instance of
PrettyPrinter - Save formatted string output instead of printing it
- Print and recognize recursive data structures
Along the way, you’ll also see an HTTP request to a public API and JSON parsing in action.
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Understanding the Need for Python’s Pretty Print
The Python pprint module is helpful in many situations. It comes in handy when making API requests, dealing with JSON files, or handling complicated and nested data. You’ll probably find that using the normal print() function isn’t adequate to efficiently explore your data and debug your application. When you use print() with dictionaries and lists, the output doesn’t contain any newlines.
Before you start exploring pprint, you’ll first use urllib to make a request to get some data. You’ll make a request to {JSON} Placeholder for some mock user information. The first thing to do is to make the HTTP GET request and put the response into a dictionary:
>>> from urllib import request
>>> response = request.urlopen("https://jsonplaceholder.typicode.com/users")
>>> json_response = response.read()
>>> import json
>>> users = json.loads(json_response)
Here, you make a basic GET request and then parse the response into a dictionary with json.loads(). With the dictionary now in a variable, a common next step is to print the contents with print():
>>> print(users)
[{'id': 1, 'name': 'Leanne Graham', 'username': 'Bret', 'email': 'Sincere@april.biz', 'address': {'street': 'Kulas Light', 'suite': 'Apt. 556', 'city': 'Gwenborough', 'zipcode': '92998-3874', 'geo': {'lat': '-37.3159', 'lng': '81.1496'}}, 'phone': '1-770-736-8031 x56442', 'website': 'hildegard.org', 'company': {'name': 'Romaguera-Crona', 'catchPhrase': 'Multi-layered client-server neural-net', 'bs': 'harness real-time e-markets'}}, {'id': 2, 'name': 'Ervin Howell', 'username': 'Antonette', 'email': 'Shanna@melissa.tv', 'address': {'street': 'Victor Plains', 'suite': 'Suite 879', 'city': 'Wisokyburgh', 'zipcode': '90566-7771', 'geo': {'lat': '-43.9509', 'lng': '-34.4618'}}, 'phone': '010-692-6593 x09125', 'website': 'anastasia.net', 'company': {'name': 'Deckow-Crist', 'catchPhrase': 'Proactive didactic contingency', 'bs': 'synergize scalable supply-chains'}}, {'id': 3, 'name': 'Clementine Bauch', 'username': 'Samantha', 'email': 'Nathan@yesenia.net', 'address': {'street': 'Douglas Extension', 'suite': 'Suite 847', 'city': 'McKenziehaven', 'zipcode': '59590-4157', 'geo': {'lat': '-68.6102', 'lng': '-47.0653'}}, 'phone': '1-463-123-4447', 'website': 'ramiro.info', 'company': {'name': 'Romaguera-Jacobson', 'catchPhrase': 'Face to face bifurcated interface', 'bs': 'e-enable strategic applications'}}, {'id': 4, 'name': 'Patricia Lebsack', 'username': 'Karianne', 'email': 'Julianne.OConner@kory.org', 'address': {'street': 'Hoeger Mall', 'suite': 'Apt. 692', 'city': 'South Elvis', 'zipcode': '53919-4257', 'geo': {'lat': '29.4572', 'lng': '-164.2990'}}, 'phone': '493-170-9623 x156', 'website': 'kale.biz', 'company': {'name': 'Robel-Corkery', 'catchPhrase': 'Multi-tiered zero tolerance productivity', 'bs': 'transition cutting-edge web services'}}, {'id': 5, 'name': 'Chelsey Dietrich', 'username': 'Kamren', 'email': 'Lucio_Hettinger@annie.ca', 'address': {'street': 'Skiles Walks', 'suite': 'Suite 351', 'city': 'Roscoeview', 'zipcode': '33263', 'geo': {'lat': '-31.8129', 'lng': '62.5342'}}, 'phone': '(254)954-1289', 'website': 'demarco.info', 'company': {'name': 'Keebler LLC', 'catchPhrase': 'User-centric fault-tolerant solution', 'bs': 'revolutionize end-to-end systems'}}, {'id': 6, 'name': 'Mrs. Dennis Schulist', 'username': 'Leopoldo_Corkery', 'email': 'Karley_Dach@jasper.info', 'address': {'street': 'Norberto Crossing', 'suite': 'Apt. 950', 'city': 'South Christy', 'zipcode': '23505-1337', 'geo': {'lat': '-71.4197', 'lng': '71.7478'}}, 'phone': '1-477-935-8478 x6430', 'website': 'ola.org', 'company': {'name': 'Considine-Lockman', 'catchPhrase': 'Synchronised bottom-line interface', 'bs': 'e-enable innovative applications'}}, {'id': 7, 'name': 'Kurtis Weissnat', 'username': 'Elwyn.Skiles', 'email': 'Telly.Hoeger@billy.biz', 'address': {'street': 'Rex Trail', 'suite': 'Suite 280', 'city': 'Howemouth', 'zipcode': '58804-1099', 'geo': {'lat': '24.8918', 'lng': '21.8984'}}, 'phone': '210.067.6132', 'website': 'elvis.io', 'company': {'name': 'Johns Group', 'catchPhrase': 'Configurable multimedia task-force', 'bs': 'generate enterprise e-tailers'}}, {'id': 8, 'name': 'Nicholas Runolfsdottir V', 'username': 'Maxime_Nienow', 'email': 'Sherwood@rosamond.me', 'address': {'street': 'Ellsworth Summit', 'suite': 'Suite 729', 'city': 'Aliyaview', 'zipcode': '45169', 'geo': {'lat': '-14.3990', 'lng': '-120.7677'}}, 'phone': '586.493.6943 x140', 'website': 'jacynthe.com', 'company': {'name': 'Abernathy Group', 'catchPhrase': 'Implemented secondary concept', 'bs': 'e-enable extensible e-tailers'}}, {'id': 9, 'name': 'Glenna Reichert', 'username': 'Delphine', 'email': 'Chaim_McDermott@dana.io', 'address': {'street': 'Dayna Park', 'suite': 'Suite 449', 'city': 'Bartholomebury', 'zipcode': '76495-3109', 'geo': {'lat': '24.6463', 'lng': '-168.8889'}}, 'phone': '(775)976-6794 x41206', 'website': 'conrad.com', 'company': {'name': 'Yost and Sons', 'catchPhrase': 'Switchable contextually-based project', 'bs': 'aggregate real-time technologies'}}, {'id': 10, 'name': 'Clementina DuBuque', 'username': 'Moriah.Stanton', 'email': 'Rey.Padberg@karina.biz', 'address': {'street': 'Kattie Turnpike', 'suite': 'Suite 198', 'city': 'Lebsackbury', 'zipcode': '31428-2261', 'geo': {'lat': '-38.2386', 'lng': '57.2232'}}, 'phone': '024-648-3804', 'website': 'ambrose.net', 'company': {'name': 'Hoeger LLC', 'catchPhrase': 'Centralized empowering task-force', 'bs': 'target end-to-end models'}}]
Oh dear! One huge line with no newlines. Depending on your console settings, this might appear as one very long line. Alternatively, your console output might have its word-wrapping mode on, which is the most common situation. Unfortunately, that doesn’t make the output much friendlier!
If you look at the first and last characters, you can see that this appears to be a list. You might be tempted to start writing a loop to print the items:
for user in users:
print(user)
This for loop would print each object on a separate line, but even then, each object takes up way more space than can fit on a single line. Printing in this way does make things a bit better, but it’s by no means ideal. The above example is a relatively simple data structure, but what would you do with a deeply nested dictionary 100 times the size?
Sure, you could write a function that uses recursion to find a way to print everything. Unfortunately, you’ll likely run into some edge cases where this won’t work. You might even find yourself writing a whole module of functions just to get to grips with the structure of the data!
Enter the pprint module!
Working With pprint
pprint is a Python module made to print data structures in a pretty way. It has long been part of the Python standard library, so installing it separately isn’t necessary. All you need to do is to import its pprint() function:
>>> from pprint import pprint
Then, instead of going with the normal print(users) approach as you did in the example above, you can call your new favorite function to make the output pretty:
>>> pprint(users)
This function prints users—but in a new-and-improved pretty way:
>>> pprint(users)
[{'address': {'city': 'Gwenborough',
'geo': {'lat': '-37.3159', 'lng': '81.1496'},
'street': 'Kulas Light',
'suite': 'Apt. 556',
'zipcode': '92998-3874'},
'company': {'bs': 'harness real-time e-markets',
'catchPhrase': 'Multi-layered client-server neural-net',
'name': 'Romaguera-Crona'},
'email': 'Sincere@april.biz',
'id': 1,
'name': 'Leanne Graham',
'phone': '1-770-736-8031 x56442',
'username': 'Bret',
'website': 'hildegard.org'},
{'address': {'city': 'Wisokyburgh',
'geo': {'lat': '-43.9509', 'lng': '-34.4618'},
'street': 'Victor Plains',
'suite': 'Suite 879',
'zipcode': '90566-7771'},
'company': {'bs': 'synergize scalable supply-chains',
'catchPhrase': 'Proactive didactic contingency',
'name': 'Deckow-Crist'},
'email': 'Shanna@melissa.tv',
'id': 2,
'name': 'Ervin Howell',
'phone': '010-692-6593 x09125',
'username': 'Antonette',
'website': 'anastasia.net'},
...
{'address': {'city': 'Lebsackbury',
'geo': {'lat': '-38.2386', 'lng': '57.2232'},
'street': 'Kattie Turnpike',
'suite': 'Suite 198',
'zipcode': '31428-2261'},
'company': {'bs': 'target end-to-end models',
'catchPhrase': 'Centralized empowering task-force',
'name': 'Hoeger LLC'},
'email': 'Rey.Padberg@karina.biz',
'id': 10,
'name': 'Clementina DuBuque',
'phone': '024-648-3804',
'username': 'Moriah.Stanton',
'website': 'ambrose.net'}]
Read the full article at https://realpython.com/python-pretty-print/ »
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