pprint(): how to use double quotes to display strings?

Question

If I print a dictionary using pprint, it always wraps strings around single quotes ('):

>>> from pprint import pprint
>>> pprint({'AAA': 1, 'BBB': 2, 'CCC': 3})
{'AAA': 1, 'BBB': 2, 'CCC': 3}

Is there any way to tell pprint to use double quotes (") instead? I would like to have the following behaviour:

>>> from pprint import pprint
>>> pprint({'AAA': 1, 'BBB': 2, 'CCC': 3})
{"AAA": 1, "BBB": 2, "CCC": 3}

Asked By: E.Z.

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Source

Answer 1

It looks like you are trying to produce JSON; if so, use the json module:

>>> import json
>>> print json.dumps({'AAA': 1, 'BBB': 2, 'CCC': 3})
{"AAA": 1, "BBB": 2, "CCC": 3}

The pprint() function produces Python representations, not JSON and quoting styles are not configurable. Don’t confuse the two syntaxes. JSON may at first glance look a lot like Python but there are more differences than just quoting styles:

JSON is limited to a few specific types only ({...} objects with key-value pairs, [...] arrays, "..." strings, numbers, booleans and nulls). Python data structures are far richer.
Python dictionary keys can be any hashable object, JSON object keys can only ever be strings.
JSON booleans are written in lowercase,true and false. Python uses title-case, True and False.
JSON uses null to signal the absence of a value, Python uses None.
JSON strings use UTF-16 codepoints, any non-BMP codepoint is encoded using surrogate pairs. Apart from a handful of single-letter backslash escapes such as n and " arbitrary codepoint escapes use uXXXX 16-bit hexadecimal notation. Python 3 strings cover all of Unicode, and the syntax supports xXX, uXXXX, and UXXXXXXXX 8, 16 and 32-bit escape sequences.

If you want to produce indented JSON output (a bit like pprint() outputs indented Python syntax for lists and dictionaries), then add indent=4 and sort_keys=True to the json.dumps() call:

>>> print json.dumps({'AAA': 1, 'CCC': 2, 'BBB': 3}, indent=4, sort_keys=True)
{
    "AAA": 1,
    "BBB": 2,
    "CCC": 3
}

See http://stackoverflow.com/questions/12943819/how-to-python-prettyprint-a-json-file

Answered By: Martijn Pieters

Answer 2

I see that the OP wanted JSON, but I do not want JSON and pprint is so close to giving me what I do want: black-compatible Python source, which requires that I use " instead of '.

I settled on .replace("'", '"') with pformat(), although this is both ugly and fragile ☹️:

import pprint

# Note: my code auto-generates my_dict parsing a file (not black-formatted here)
my_dict = ["spam", "eggs", "lumberjack", "knights", "ni", "eggs", "lumberjack", "knights", "ni"]

pprinter = pprint.PrettyPrinter(indent=4)
formatted_code = (
    pprinter.pformat(my_dict)
    .replace("[ ", "[n  ")  # break after opening bracket
    .replace("']", "',n]")  # break before closing bracket, add comma
    .replace("'", '"')  # use double quotes
)
with open("example_module.py", "w", encoding="utf-8") as outfile:
    outfile.write('"""Module containing auto-generated ALL_MR_HEADERS."""n')
    outfile.write(f"ALL_MR_HEADERS = {formatted_code}n")

The resulting example_module.py is black-compliant.

Answered By: sage

Answer 3

While I’m against using modules for simple things, but over the time pprint is becoming useless and not catching up with the Python 3 evolution. At least they could have added this option as a parameter.

So take advantage of the black module that prints your objects in pretty format already.

Here is the code,

import black
print(black.format_file_contents(str(D), fast=False, mode=black.FileMode()))

Will print

 '{"AAA": 1, "BBB": 2, "CCC": 3}'

Answered By: nehem

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