How to remove whitespaces and newlines from every value in a JSON file?

Parse the file using JSON:

import json
file = file.replace('\n', '')    # do your cleanup here
data = json.loads(file)

then walk through the resulting data structure.

Now I want to strip off all he whitespaces and newlines for every value in the JSON file

Using pkgutil.simplegeneric() to create a helper function get_items():

import json
import sys
from pkgutil import simplegeneric

@simplegeneric
def get_items(obj):
    while False: # no items, a scalar object
        yield None

@get_items.register(dict)
def _(obj):
    return obj.items() # json object. Edit: iteritems() was removed in Python 3

@get_items.register(list)
def _(obj):
    return enumerate(obj) # json array

def strip_whitespace(json_data):
    for key, value in get_items(json_data):
        if hasattr(value, 'strip'): # json string
            json_data[key] = value.strip()
        else:
            strip_whitespace(value) # recursive call


data = json.load(sys.stdin) # read json data from standard input
strip_whitespace(data)
json.dump(data, sys.stdout, indent=2)

Note: functools.singledispatch() function (Python 3.4+) would allow to use collections' MutableMapping/MutableSequence instead of dict/list here.

Output

{
  "anotherName": [
    {
      "anArray": [
        {
          "anotherKey": "value", 
          "key": "value"
        }, 
        {
          "anotherKey": "value", 
          "key": "value"
        }
      ]
    }
  ], 
  "name": [
    {
      "someKey": "some Value"
    }, 
    {
      "someKey": "another value"
    }
  ]
}