prettyjson.py

import types

def prettyjson(obj, indent=2, maxlinelength=80):
    """Renders JSON content with indentation and line splits/concatenations to fit maxlinelength.
    Only dicts, lists and basic types are supported"""

    items, _ = getsubitems(obj, itemkey="", islast=True, maxlinelength=maxlinelength)
    res = indentitems(items, indent, indentcurrent=0)
    return res


def getsubitems(obj, itemkey, islast, maxlinelength):
    items = []
    can_concat = True      # assume we can concatenate inner content unless a child node returns an expanded list

    isdict = isinstance(obj, dict)
    islist = isinstance(obj, list)
    istuple = isinstance(obj, tuple)

    # building json content as a list of strings or child lists
    if isdict or islist or istuple:
        if isdict: opening, closing, keys = ("{", "}", iter(obj.keys()))
        elif islist: opening, closing, keys = ("[", "]", range(0, len(obj)))
        elif istuple: opening, closing, keys = ("[", "]", range(0, len(obj)))    # tuples are converted into json arrays

        if itemkey != "": opening = itemkey + ": " + opening
        if not islast: closing += ","

        # Get list of inner tokens as list
        count = 0
        subitems = []
        itemkey = ""
        for k in keys:
            count += 1
            islast_ = count == len(obj)
            itemkey_ = ""
            if isdict: itemkey_ = basictype2str(k)
            inner, can_concat_ = getsubitems(obj[k], itemkey_, islast_, maxlinelength)    # inner = (items, indent)
            subitems.extend(inner)                      # inner can be a string or a list
            can_concat = can_concat and can_concat_     # if a child couldn't concat, then we are not able either

        # atttempt to concat subitems if all fit within maxlinelength
        if (can_concat):
            totallength = 0
            for item in subitems:
                totallength += len(item)
            totallength += len(subitems)-1     # spaces between items
            if (totallength <= maxlinelength): 
                str = ""
                for item in subitems:
                    str += item + " "      # add space between items, comma is already there
                str = str.strip()
                subitems = [ str ]         # wrap concatenated content in a new list
            else:
                can_concat = False

        # attempt to concat outer brackets + inner items
        if (can_concat):
            if (len(opening) + totallength + len(closing) <= maxlinelength):
                items.append(opening + subitems[0] + closing)
            else:
                can_concat = False
                
        if (not can_concat):
            items.append(opening)       # opening brackets
            items.append(subitems)      # Append children to parent list as a nested list
            items.append(closing)       # closing brackets

    else:
        # basic types
        strobj = itemkey
        if strobj != "": strobj += ": "
        strobj += basictype2str(obj)
        if not islast: strobj += ","
        items.append(strobj)
    
    return items, can_concat


def basictype2str(obj):
    if isinstance (obj, str):
        strobj = "\"" + str(obj) + "\""
    elif isinstance(obj, bool): 
        strobj = { True: "true", False: "false" }[obj]
    else:
        strobj = str(obj)
    return strobj


def indentitems(items, indent, indentcurrent):
    """Recursively traverses the list of json lines, adds indentation based on the current depth"""
    res = ""
    indentstr = " " * indentcurrent
    for item in items:
        if (isinstance(item, list)): 
            res += indentitems(item, indent, indentcurrent + indent)
        else:
            res += indentstr + item + "\n"
    return res