6. File conversions

For json formatting and conversions see: https://jsonformatter.org/

For xml formatting and conversion see: https://jsonformatter.org/xml-formatter

6.1. Files for csv ⇔ json

Download the csv file months.csv

Download the json file months.json

6.2. json file to csv file

json is flexible in its structure.
Each particular json file structure will have a different conversion to csv.
The json stucture below is based on a simplified structure as {mainkey:[dictionaries]}.
The months json follows that structrue.
Each object in the array will become a row in csv.

{"months":
[{"Month":"January","Abbr":"Jan","Numeric":"1"},
...
{"Month":"December","Abbr":"Dec","Numeric":"12"}]
}

csv file contents

Month,Abbr,Numeric
January,Jan,1
...
December,Dec,12

Some parts of the code need some explanation:

j_key = list(json_data.keys())[0] gets the key: “months”.
json_data.keys() return a dict object withe the key.
list(json_data.keys()) converts the dict object to a list.
list(json_data.keys())[0] gives the key value “months” which will be needed to get the fieldnames for the csv DictWriter.

fieldnames = list(json_data[j_key][0].keys()) gets the fieldnames for the csv DictWriter, where j_key is “months”.
json_data[j_key] gives the array of dictionaries for each employee. These are listed below in the [].
json_data[j_key][0] gives the first employee dictionary: {“firstName”:”John”,”lastName”:”Doe”,”gender”:”Male”}.
json_data[j_key][0].keys() gives a dict keys object.
list(json_data[j_key][0].keys()) converts the dict keys object into a list.

The dictionary elements of the json array are iterated over by: for row in json_data[j_key], where j_key is “months”.

import json
import csv

json_path = "files/months.json"
csv_path = "files/months2.csv"

with open(json_path, "r") as f:
    json_data = json.load(f)

    j_key = list(json_data.keys())[0]
    fieldnames = list(json_data[j_key][0].keys())

    with open(csv_path, 'w', newline='') as new_file:
        csv_writer = csv.DictWriter(new_file, fieldnames=fieldnames)
        csv_writer.writeheader()
        for row in json_data[j_key]:
            csv_writer.writerow(row)

Tasks

Write a definition to do the conversion from a json file to a csv file.

6.3. csv file to json file

See: https://pythonexamples.org/python-csv-to-json/
The csv needs a header row.
The json will take the form of a python dictionary: json_dict = {json_mainkey: json_array}
The csv.DictReader will be used to append each row of the csv to an array, json_array.

import csv
import json


csv_path = "files/months.csv"
json_path = "files/months2.json"
json_mainkey = "months"
json_array = []
with open(csv_path, 'r', newline='') as csv_file:
    csv_reader = csv.DictReader(csv_file)
    for row in csv_reader:
        json_array.append(row)

json_dict = {json_mainkey: json_array}
with open(json_path, 'w', encoding='utf-8') as jsonf:
    json_str= json.dumps(json_dict, indent=4)
    jsonf.write(json_str)

Tasks

Write a definition to do the conversion from a csv file to a json file.

6.4. Files for xml ⇔ json

Download the months csv file employees.xml

Download the months json file employees.json

6.5. Module for xml conversions

pip install xmltodict from the terminal first so that file converions involving xml can be done.

See: https://pypi.org/project/xmltodict/

6.6. xml file to json file

The function xml_to_json_file(xml_file_path, json_file_path) takes a path to an xml file and a path to a json file.
There are two conversion steps: convert an xml string to a dictionary via py_dict = xmltodict.parse(xml_str).
Then from a dictionary to a json file via json.dump(py_dict, f, indent=4).

import json
import xmltodict


def xml_to_json_file(xml_file_path, json_file_path):
    with open(xml_file_path) as f:
        xml_str = f.read()
    py_dict = xmltodict.parse(xml_str)
    with open(json_file_path, 'w') as f:
        json.dump(py_dict, f, indent=4)


xml_file_path = "files/employees.xml"
json_file_path = "files/convert_xml_to_json.json"

xml_to_json_file(xml_file_path, json_file_path)

6.7. json file to xml file

xmltodict needs to construct the JSON with the very first key as the root XML tag.

This means that there should only be a single JSON key at the root level of data.

The function json_to_xml_file(json_file_path, xml_file_path) takes a path to a json file and a path to an xml file.

The line xml_str = xmltodict.unparse(json_data, pretty=True) converts the json as a dictionary to an xml string.

import json
import xmltodict

def json_to_xml_file(json_file_path, xml_file_path):
    with open(json_file_path, "r") as f:
        json_dict = json.load(f)
        xml_str = xmltodict.unparse(json_dict, pretty=True)
    with open(xml_file_path, "w") as f2:
        f2.write(xml_str)


json_file_path = "files/employees.json"
xml_file_path = "files/convert_json_to_xml.xml"

json_to_xml_file(json_file_path, xml_file_path)