pprint dictionary on multiple lines

Question

I'm trying to get a pretty print of a dictionary, but I'm having no luck:

>>> import pprint
>>> a = {'first': 123, 'second': 456, 'third': {1:1, 2:2}}
>>> pprint.pprint(a)
{'first': 123, 'second': 456, 'third': {1: 1, 2: 2}}

I wanted the output to be on multiple lines, something like this:

{'first': 123,
 'second': 456,
 'third': {1: 1,
           2: 2}
}

Can pprint do this? If not, then which module does it? I'm using Python 2.7.3.

Lipread

Does this answer your question? How to pretty print nested dictionaries? – Henceforward

@Henceforward not quite. The desired output in that question is not the same as mine is here – Lipread

Answer 1

Use width=1 or width=-1:

In [33]: pprint.pprint(a, width=1)
{'first': 123,
 'second': 456,
 'third': {1: 1,
           2: 2}}

Aristotelianism

What do negative widths do? – Dyche

@Tim: I just tried it, and it worked, but I don't know if that is documented somewhere. – Aristotelianism

Negative widths don't do anything special. As the code goes along, it checks to see if the length of the partial output string is < width. Any negative width just means the answer will always be "no". A width of 0 will almost always (or maybe always - I don't care enough to think about perverse cases ;-)) do the same. – Moribund

@TimPeters: Yeah, I took a look at the source. There is a check for width==0 (it raises an error), but it seems that 0 could be treated the same as a negative value--always answer "no", as you put it--with no harm. – Aristotelianism

Answer 2

You could convert the dict to json through json.dumps(d, indent=4)

import json

print(json.dumps(item, indent=4))
{
    "second": 456,
    "third": {
        "1": 1,
        "2": 2
    },
    "first": 123
}

Literalminded

Much prettier than the other solutions – Prescript

@ErikAronesty While you should pay attention to the null and boolean values (true/false). They are JSON values not the python objects. – Literalminded

Okay solution for simple cases, but converts python values to json values (as @RyanChou pointed out) and it might not be desirable or possible (like with datetime): json.dumps({'d': datetime.now()}) will crash with Object of type datetime is not JSON serializable. – Patty

NameError: name 'json' is not defined - Is this a module that needs importing? If so, would you mind updating your answer to reflect that? – Ranson

Answer 3

If you are trying to pretty print the environment variables, use:

pprint.pprint(dict(os.environ), width=1)

Hutchings

Answer 4

Two things to add on top of Ryan Chou's already very helpful answer:

• pass the sort_keys argument for an easier visual grok on your dict, esp. if you're working with pre-3.6 Python (in which dictionaries are unordered)

print(json.dumps(item, indent=4, sort_keys=True))
"""
{
    "first": 123,
    "second": 456,
    "third": {
        "1": 1,
        "2": 2
    }
}
"""

• dumps() will only work if the dictionary keys are primitives (strings, int, etc.)

Tambourin

Neat! sort_keys is a great argument. Unfortunately, as you say not always applicable: TypeError: Object of type Tag is not JSON serializable... – Emarie

Answer 5

This is a Copy-Pasta for testing purposes and to help with a usage example.

from pprint import pprint  # I usually only need this module from the package. 

a = {'first': 123, 'second': 456, 'third': {1:1, 2:2}, 'zfourth': [{3:9, 7:8}, 'distribution'], 1:2344, 2:359832, 3:49738428, 4:'fourth', 5:{'dictionary':'of things', 'new':['l','i','s','t']}}

pprint(dict(a), indent=4, width=1)

# Wrap your variable in dict() function
# Optional: indent=4. for readability
# Required: width=1 for wrapping each item to its own row.
# Note: Default pprint is to sort the dictionary
# Note: This also auto-wraps anything sting that has spaces in it.  See 'of things' below.

# Documentation:  https://docs.python.org/3/library/pprint.html
# Examples:       https://pymotw.com/2/pprint/
# Blog:           https://realpython.com/python-pretty-print/

Provides the following result:

{   1: 2344,
    2: 359832,
    3: 49738428,
    4: 'fourth',
    5: {   'dictionary': 'of '
                         'things',
           'new': [   'l',
                      'i',
                      's',
                      't']},
    'first': 123,
    'second': 456,
    'third': {   1: 1,
                 2: 2},
    'zfourth': [   {   3: 9,
                       7: 8},
                   'distribution']}

Porphyria

I don't understand how this is intended to a) answer the question; b) add any information that isn't thoroughly covered by existing answers. – Diligence

This helps as it is just a different perspective with a copy paste option. As sometimes snippets do not exactly convey the point to new learners. – Porphyria