You can do this on the command line:

python3 -m json.tool some.json

(as already mentioned in the commentaries to the question, thanks to @Kai Petzke for the python3 suggestion).

Actually python is not my favourite tool as far as json processing on the command line is concerned. For simple pretty printing is ok, but if you want to manipulate the json it can become overcomplicated. You'd soon need to write a separate script-file, you could end up with maps whose keys are u"some-key" (python unicode), which makes selecting fields more difficult and doesn't really go in the direction of pretty-printing.

You can also use jq:

jq . some.json

and you get colors as a bonus (and way easier extendability).

Addendum: There is some confusion in the comments about using jq to process large JSON files on the one hand, and having a very large jq program on the other. For pretty-printing a file consisting of a single large JSON entity, the practical limitation is RAM. For pretty-printing a 2GB file consisting of a single array of real-world data, the "maximum resident set size" required for pretty-printing was 5GB (whether using jq 1.5 or 1.6). Note also that jq can be used from within python after pip install jq.

I don't see how you could do it in the json.dumps. After a bit of searching I came across a few options: One option would be to do some post-processing with a custom function:

def fix_json_indent(text, indent=3):
            space_indent = indent * 4
    initial = " " * space_indent
    json_output = []
    current_level_elems = []
    all_entries_at_level = None  # holder for consecutive entries at exact space_indent level
    for line in text.splitlines():
        if line.startswith(initial):
            if line[space_indent] == " ":
                # line indented further than the level
                if all_entries_at_level:
                    current_level_elems.append(all_entries_at_level)
                    all_entries_at_level = None
                item = line.strip()
                current_level_elems.append(item)
                if item.endswith(","):
                    current_level_elems.append(" ")
            elif current_level_elems:
                # line on the same space_indent level
                # no more sublevel_entries 
                current_level_elems.append(line.strip())
                json_output.append("".join(current_level_elems))
                current_level_elems = []
            else:
                # line at the exact space_indent level but no items indented further
                if all_entries_at_level:
                    # last pending item was not the start of a new sublevel_entries.
                    json_output.append(all_entries_at_level)
                all_entries_at_level = line.rstrip()
        else:
            if all_entries_at_level:
                json_output.append(all_entries_at_level)
                all_entries_at_level = None
            if current_level_elems:
                json_output.append("".join(current_level_elems))
            json_output.append(line)
    return "\n".join(json_output)

Another possibility is a regex but it is quite ugly and depends on the structure of the code you posted:

def fix_json_indent(text):
    import re
    return  re.sub('{"', '{\n"', re.sub('\[\[', '[\n[', re.sub('\]\]', ']\n]', re.sub('}', '\n}', text))))

Ok, coded myself. Some hacks to print \n instead of real linefeed.

def fwriteKeyVals(data, f, indent=0):
    if isinstance(data, list):
        try:
            gotdata = isinstance(data[0], list)
        except IndexError:
            gotdata = False

        if gotdata:

            f.write( "\n" + "    " * indent + "[" )  
            for i in range(len(data) ):  
                if ( i == 0):
                    f.write( "[" )  
                else:
                    f.write( "    " * indent + " [" )
                for j in range(len(data[0])):  
                    f.write( "%3d" % data[i][j] )  
                    f.write( "," ) if j != len(data[0])-1 else (f.write( "]," ) if i != len(data)-1 else f.write( "]" ))  
                f.write( "\n" ) if i != len(data)-1 else f.write( "]" )  
        else:
            try:
                gotdata = data[0]
            except IndexError:
                gotdata = 'False'

            if gotdata is not 'False':
                f.write( " [" ) 
                for i in range(len(data) ): 
                    if isinstance(data[i], Number):
                        f.write( "%3d" % data[i] )   
                    else:
                        dataListLf = data[i].split("\n")
                        dataToWrite = dataListLf[0]
                        for line in dataListLf[1:]:
                            dataToWrite += '\\n'+line

                        f.write( "\"" + dataToWrite + "\"")
                    f.write( "," ) if i != len(data)-1 else f.write( "]" )
            else:
                f.write( " [\"\"]" )