export some item from one json file to new file.

json_export.py

import json
import codecs

#open the source file
json_file = open('map.txt','r')
data = json_file.read()
datas = json.loads(data.decode("utf-8" ) )
#data1 = json.loads(json_file.read())#.decode('utf-8') )
# data.decode("utf-8-sig"))
#print data

print type(datas)

map_units = datas["units_inst"]

print type(map_units)

targetmap = "map_3"

out_units = []

for unit in map_units:
    if( unit["map_name"] == targetmap):
        out_units.append(unit)
print len(out_units)

#out put wanted units to template data..

out_dicts = {"units_inst": out_units}

output_file = codecs.open("output_file.json", "w", encoding="utf-8",buffering=0)
json.dump(out_dicts, output_file, indent=2, sort_keys=True, ensure_ascii=False)

print "done"
        
#confirm file ok.
json_file2 = open("output_file.json",'r')
data = json_file2.read()
datas = json.loads(data.decode("utf-8"))
print len(datas["units_inst"])

This is my implementation to convert any kind of encoding to UTF-8 without BOM and replacing windows enlines by universal format:

def utf8_converter(file_path, universal_endline=True):
'''
Convert any type of file to UTF-8 without BOM
and using universal endline by default.

Parameters
----------
file_path : string, file path.
universal_endline : boolean (True),
                    by default convert endlines to universal format.
'''

# Fix file path
file_path = os.path.realpath(os.path.expanduser(file_path))

# Read from file
file_open = open(file_path)
raw = file_open.read()
file_open.close()

# Decode
raw = raw.decode(chardet.detect(raw)['encoding'])
# Remove windows end line
if universal_endline:
    raw = raw.replace('\r\n', '\n')
# Encode to UTF-8
raw = raw.encode('utf8')
# Remove BOM
if raw.startswith(codecs.BOM_UTF8):
    raw = raw.replace(codecs.BOM_UTF8, '', 1)

# Write to file
file_open = open(file_path, 'w')
file_open.write(raw)
file_open.close()
return 0

Call this to remove bom header of utf-8 file

import codecs
import shutil
import sys

s = sys.stdin.read(3)
if s != codecs.BOM_UTF8:
sys.stdout.write(s)

shutil.copyfileobj(sys.stdin, sys.stdout)

named it as remove_bom.py

how this code is work? $ remove_bom.py < input.txt > output.txt