如何在Python中使用JSON从文件的特定列表中检索特定字符串

Question

I got code that actually saves three different data strings in the same list. Each list is separated and I'm not even sure if that made sense... So I'm going to just paste the code:

    filename = "datosdeusuario.txt"
    leyendo = open(filename, 'r+')
    buffer = leyendo.read()
    leyendo.close()
    if not user.name in buffer:
      escribiendo = open(filename, 'a')
      escribiendo.write(json.dumps([user.name, string2, string3])+"\n")
      escribiendo.close()
      print(str(horaactual)[:19] + ": Data from " + user.name + " added")

That code is saving information like this (and working almost perfect):

["saelyth", "thisisanexampleforstring2", "andthisisanexampleforstring3"]
["anothername", "thisisanothernexampleforstring2", "andthisisanotherexampleforstring3"]
["John Connor", "exampleforstring2", "exampleforstring3"]

So my actual question and problem is... What is the best way to get an specific string from that file?

For example, let's say I want to retrieve the first string, the second string and the third string only if the user.name is John Connor (I mean, all three values from the list where the name is found). I can't seem to find a proper way to do it googling. The expected code would be something like this:

if user.name is in found in any list(position1) of the file datosdeusuario.txt
then
retrieveddata1 = List where value1 is user.name(get value1)
retrieveddata2 = List where value1 is user.name(get value2)
retrieveddata3 = List where value1 is user.name(get value3)

I have no idea how to do that. That's why I just made up that code to explain the situation.

Answer 1

I am not sure if this is what you want but:

filename = "datosdeusuario.txt"
f = open(filename,"r")
filedata = f.read()
f.close()
sp1 = filedata.split("\n")
a = ""
for x in sp1:
    if "joao m" in x:
        a = x
if(len(a) > 0):
    sp2 = a.split('"')
    values = []
    for x in sp2:
        if not(x == ", " or x == "]" or x == "[" or len(x) == 0):
            values.append(x)
    print values[0] #should by the name
    print values[1] #value 2
    print values[2] #value 3       
else: #No username in the file
    #do something
    pass

Answer 2

Maybe this would work:

retrieveddata1 = retrieveddata2 = retrieveddata3 = None
filename = "datosdeusuario.txt"
for line in open(filename, 'r'):
    retrieved = json.loads(line)
    if retrieved[0] == 'jonh connor':
        retrieveddata1 = retrieved[0]
        retrieveddata2 = retrieved[1]
        retrieveddata3 = retrieved[2]
        break

Answer 3

I suggest that you use the general solution to the problem of extracting data from JSON objects, namely jsonpath. PyPi has this library https://pypi.python.org/pypi/jsonpath/

if jsonpath.jsonpath(jsondata,'$[0]') == 'John Connor':
    result = jsonpath.jsonpath(jsondata,'$[2]')

Yes, the documentation for the Python library sucks but the code is straightforward to read through, and JSONPATH expressions are documented fairly well by other implementors.

Consider making your code clearer by adding something like:

NAME = '$[0]'
STUFF = '$[1]'
OTHERSTUFF = '$[2]'