Easily Understand Python pprint Function - Explained

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Prettify Your Data Structures With Pretty Print in Python

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.

Understanding the Need for Python’s Pretty Print

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)

When you run the above code, the output will not be easy to read. It will be a single horizontal line containing all the data. To make the output more readable, you can use the pprint module.

Working With pprint

To use the pprint module, you need to import it first:

import pprint

Now, instead of using print(), you can use pprint.pprint():

pprint.pprint(users)

When you run the code, the output will be indented and formatted in a more readable way. Each item in the dictionary will be on a separate line, making it easier to view the data.

Exploring Optional Parameters of pprint()

The pprint() function has several optional parameters that you can use to customize the output further. Here are some of the most commonly used parameters:

Summarizing Your Data: depth

The depth parameter allows you to limit the depth to which pprint will recurse. By default, it’s set to None, which means it will recurse to any depth. If you only want to display a certain depth of your data, you can set the depth parameter accordingly:

pprint.pprint(users, depth=2)

Giving Your Data Space: indent

The indent parameter specifies the number of spaces to use for each level of indentation. By default, it’s set to 1. If you want to increase or decrease the level of indentation, you can set the indent parameter accordingly:

pprint.pprint(users, indent=4)

Limiting Your Line Lengths: width

The width parameter specifies the maximum number of characters to display per line. By default, it’s set to 80. If you want to adjust the maximum line length, you can set the width parameter accordingly:

pprint.pprint(users, width=100)

Squeezing Your Long Sequences: compact

The compact parameter determines how to display long sequences, such as lists and tuples. When set to True, it displays the entire sequence in a single line. When set to False, it breaks the sequence into multiple lines. By default, it’s set to False. If you want to display long sequences in a single line, you can set the compact parameter to True:

pprint.pprint(users, compact=True)

Directing Your Output: stream

The stream parameter specifies the file-like object where the output should be directed. By default, it’s set to None, which means it will use sys.stdout as the output stream. If you want to direct the output to a different file-like object, you can set the stream parameter accordingly:

import sys
pprint.pprint(users, stream=sys.stderr)

Preventing Dictionary Sorting: sort_dicts

The sort_dicts parameter determines whether dictionaries should be sorted alphabetically when printing. By default, it’s set to True. If you want to preserve the original order of the dictionaries, you can set the sort_dicts parameter to False:

pprint.pprint(users, sort_dicts=False)

Prettifying Your Numbers: underscore_numbers

The underscore_numbers parameter determines whether numbers should be prettified with underscores. By default, it’s set to False. If you want to separate the digits of large numbers with underscores to make them more readable, you can set the underscore_numbers parameter to True:

pprint.pprint(users, underscore_numbers=True)

Creating a Custom PrettyPrinter Object

In addition to using the pprint() function, you can also create your own instance of the PrettyPrinter class from the pprint module. This allows you to have more control over the output formatting. Here’s an example of how you can create a custom PrettyPrinter object:

import pprint

custom_printer = pprint.PrettyPrinter(indent=4, width=80)

custom_printer.pprint(users)

By creating a custom PrettyPrinter object, you can set parameters like indent and width according to your specific requirements.

Getting a Pretty String With pformat()

In addition to printing data structures, you can also get a pretty formatted string representation of the data using the pformat() function from the pprint module. Here’s an example:

import pprint

formatted_string = pprint.pformat(users)

print(formatted_string)

The pformat() function returns a string representation of the data structure in a pretty formatted way. You can then use that string for further processing or saving it to a file.

Handling Recursive Data Structures

Recursive data structures can be challenging to print without causing infinite loops. However, the pprint module handles recursive data structures gracefully by detecting and representing them correctly. Here’s an example:

import pprint

data = {
    "name": "John Doe",
    "age": 30,
    "friends": [
        {
            "name": "Jane Smith",
            "age": 28,
            "friends": [
                {
                    "name": "Alice Johnson",
                    "age": 25,
                    "friends": []
                }
            ]
        }
    ]
}

pprint.pprint(data)

In this example, the pprint module correctly represents the recursive structure of the friends list without causing any infinite loops.

Conclusion

Python’s pprint module is a powerful tool for printing data structures in a readable and pretty format. It allows you to customize the output by using optional parameters and even create your own instance of the PrettyPrinter class. With pprint, you can easily explore complex data structures, debug your code, and make your output more human-friendly.