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# Introduction to Python: JSON
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JSON is a very important format for storing data in Software engineering. </br>
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JSON is popular for the following scenarios :
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* Popular standard for data structures in general.
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* Applications may talk to each other by passing JSON data back and forth (HTTP Web APIs).
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* Applications often store configuration in JSON format as a configuration file.
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* Data may be stored in databases or caches in JSON format.
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* DevOps engineers may store infrastructure configuration in JSON format.
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## Python Dev Environment
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The same as Part 1, we start with a [dockerfile](./dockerfile) where we declare our version of `python`.
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```
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FROM python:3.9.6-alpine3.13 as dev
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WORKDIR /work
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```
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Let's build and start our container:
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```
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cd python\introduction\part-3.json
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docker build --target dev . -t python
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docker run -it -v ${PWD}:/work python sh
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/work # python --version
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Python 3.9.6
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```
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## Our application
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Firstly we have a class to define what a customer looks like:
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```
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class Customer:
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def __init__(self, c="",f="",l=""):
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self.customerID = c
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self.firstName = f
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self.lastName = l
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def fullName(self):
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return self.firstName + " " + self.lastName
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```
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Then we need a function which returns our customers:
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```
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def getCustomers():
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customers = {
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"a": Customer("a","James", "Baker"),
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"b": Customer("b", "Jonathan", "D"),
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"c": Customer("c", "Aleem", "Janmohamed"),
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"d": Customer("d", "Ivo", "Galic"),
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"e": Customer("e", "Joel", "Griffiths"),
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"f": Customer("f", "Michael", "Spinks"),
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"g": Customer("g", "Victor", "Savkov"),
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"h" : Customer("h", "Marcel", "Dempers")
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}
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return customers
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```
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Here is a function to return a specific customer:
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```
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def getCustomer(customerID):
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customer = getCustomers()
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return customer[customerID]
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```
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Test our functions:
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```
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customers = getCustomers()
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customer = customers["h"]
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print(customers)
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print(customer.fullName)
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```
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## Files
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In [part-2](../part-2.files/README.md) we learnt about reading and writing to files. </br>
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We changed our functions to get customers from file and update customers by writing the data back to file. </br>
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Let's do that quick:
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## Get Customers
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```
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import os.path
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import csv
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def getCustomers():
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if os.path.isfile("customers.log"):
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with open('customers.log', newline='') as customerFile:
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reader = csv.DictReader(customerFile)
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l = list(reader)
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customers = {c["customerID"]: c for c in l}
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return customers
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else:
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return {}
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```
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## Update Customers
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Let's create a function to update our customers:
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```
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def updateCustomers(customers):
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fields = ['customerID', 'firstName', 'lastName']
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with open('customers.log', 'w', newline='') as customerFile:
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writer = csv.writer(customerFile)
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writer.writerow(fields)
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for customerID in customers:
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customer = customers[customerID]
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writer.writerow([customer.customerID, customer.firstName, customer.lastName])
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```
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## Test
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Let's test our two functions to ensure they work
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```
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customers = {
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"a": Customer("a","James", "Baker"),
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"b": Customer("b", "Jonathan", "D"),
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"c": Customer("c", "Aleem", "Janmohamed"),
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"d": Customer("d", "Ivo", "Galic"),
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"e": Customer("e", "Joel", "Griffiths"),
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"f": Customer("f", "Michael", "Spinks"),
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"g": Customer("g", "Victor", "Savkov"),
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"h" : Customer("h", "Marcel", "Dempers")
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}
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#save it
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updateCustomers(customers)
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#see the changes
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customers = getCustomers()
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for customer in customers:
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print(customers[customer])
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```
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## JSON
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JSON is a very simple data structure for building objects.
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you can define any type of object and data using JSON. </br>
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In JSON, objects are defined by open and close brackets, like `{}` </br>
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Arrays or lists are defined as square brackets, like `[]` </br>
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We can therefore define a customer like :
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`Notice keys and values have quotes, and separated by colon`
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```
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{
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"customerID" : "a",
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"firstName: "Bob",
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"lastName": "Smith"
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}
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```
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We can define an array of customers in JSON by declaring our array with square brackets and having customer objects inside, separated by commas:
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```
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# Example Array:
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[{customer-1},{customer-2},{customer-3},{customer-4} ]
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```
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## JSON Library
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Python provides a library for dealing with JSON. </br>
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Let's take our customer dictionary, and convert it to json structure and
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finally write it to file using our update function.
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```
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import json
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```
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Now first things first, we need to convert our customers dictionary to a JSON structured string so we can store it to file. </br>
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The `json` library allows us to convert dictionaries to files using
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the `dumps` function:
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```
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jsonData = json.dumps(customers)
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print(jsonData)
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```
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But if we run this we get an error:
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`TypeError: Object of type Customer is not JSON serializable`
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That is because the library can only deal with full dictionaries.
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Taking a closer look at our dictionary, our customer is a class.
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```
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# our key is a string
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# our value is a class
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"h" : Customer("h", "Marcel", "Dempers")
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```
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`json.dumps()` only allows full dictionaries so we need our customer object to be in dictionary form like so:
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```
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"h": { "customerID": "h", "firstName" : "Marcel", "lastName" : "Dempers"}
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```
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To fix our dictionary, we can iterate it and build a new one
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```
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# start with an empty one
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customerDict = {}
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#populate our new dictionary
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for id in customers:
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customerDict[id] = customers[id].__dict__
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#print it
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print(customerDict)
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```
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Now we can convert our customer dictionary to json
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```
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customerJSON = json.dumps(customerDict)
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print(customerJSON)
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```
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Now we've converted our data into JSON, we can view this in a new tab window and change the language mode to JSON to visualise the data in our new format.
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Now essentially our application will use dictionaries when working with the data
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but store and transport it as JSON. </br>
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Therefore our update function should take a dictionary and convert it to JSON
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and store it.
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```
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def updateCustomers(customer):
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with open('customers.json', 'w', newline='') as customerFile:
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customerJSON = json.dumps(customer)
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customerFile.write(customerJSON)
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```
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We also need to change our `getCustomers` function to read the JSON file
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and convert that data correctly back to a dictionary for processing.
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```
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def getCustomers():
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if os.path.isfile("customers.json"):
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with open('customers.json', newline='') as customerFile:
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data = customerFile.read()
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customers = json.loads(data)
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return customers
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else:
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return {}
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```
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Finally let's test our functions :
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```
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customers = getCustomers()
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print(customers)
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```
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It's also very easy to add a customer to our JSON data using our class and using pythons internal `__dict__` property to convert the object to a dictionary and add it to our customers dictionary
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```
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customers["i"] = Customer("i", "Bob", "Smith").__dict__
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updateCustomers(customers)
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```
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## Docker
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Let's build our container image and run it while mounting our customer file
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Our final `dockerfile`
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```
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FROM python:3.9.6-alpine3.13 as dev
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WORKDIR /work
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FROM dev as runtime
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COPY ./src/ /app
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ENTRYPOINT [ "python", "/app/app.py" ]
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```
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Build and run our container.
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Notice the `customers.json` file gets created if it does not exist.
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```
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cd python\introduction\part-3.json
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docker build . -t customer-app
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docker run -v ${PWD}:/work -w /work customer-app
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```
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@ -1,8 +0,0 @@
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FROM python:3.9.6-alpine3.13 as dev
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WORKDIR /work
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FROM dev as runtime
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COPY ./src/ /app
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ENTRYPOINT [ "python", "/app/app.py" ]
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@ -1,50 +0,0 @@
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import os.path
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import csv
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import json
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class Customer:
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def __init__(self, c="",f="",l=""):
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self.customerID = c
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self.firstName = f
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self.lastName = l
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def fullName(self):
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return self.firstName + " " + self.lastName
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def getCustomers():
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if os.path.isfile("customers.json"):
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with open('customers.json', newline='') as customerFile:
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data = customerFile.read()
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customers = json.loads(data)
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return customers
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else:
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return {}
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def updateCustomers(customer):
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with open('customers.json', 'w', newline='') as customerFile:
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customerJSON = json.dumps(customer)
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customerFile.write(customerJSON)
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customers = {
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"a": Customer("a","James", "Baker"),
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"b": Customer("b", "Jonathan", "D"),
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"c": Customer("c", "Aleem", "Janmohamed"),
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"d": Customer("d", "Ivo", "Galic"),
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"e": Customer("e", "Joel", "Griffiths"),
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"f": Customer("f", "Michael", "Spinks"),
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"g": Customer("g", "Victor", "Savkov"),
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"h" : Customer("h", "Marcel", "Dempers")
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}
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customerDict = {}
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for id in customers:
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customerDict[id] = customers[id].__dict__
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updateCustomers(customerDict)
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customers = getCustomers()
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customers["i"] = Customer("i", "Marcel", "Dempers").__dict__
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updateCustomers(customers)
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print(customers)
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