Day 84: Ultimate guide python data dictionary list JSON through example

JSON can be entangled into some nested gooodness

python data dictionary list json

Mmmmm…

And this is the beauty of it.

Python allows you to take any data and represent it in JSON.

But the counterpart is that it might not be straightforward to understand.

Let’s take a JSON and examine it

Raw JSON

{"e":"currency_limits","ok":"ok","data":{"pairs":[{"symbol1":"BTC","symbol2":"USD","pricePrecision":1,"minLotSize":0.0004,"minLotSizeS2":10,"maxLotSize":null,"minPrice":"3500","maxPrice":"350000"},

Beautified JSON

It’s the same .json but using jq to represent it.

{
  "e": "currency_limits",
  "ok": "ok",
  "data": {
    "pairs": [
      {
        "symbol1": "BTC",
        "symbol2": "USD",
        "pricePrecision": 1,
        "minLotSize": 0.0004,
        "minLotSizeS2": 10,
        "maxLotSize": null,
        "minPrice": "3500",
        "maxPrice": "350000"
      },

Notes

This JSON file starts with being a dictionary.
It has 3 key value pairs

Convert json file to dictionary

import json

#we init an empty dictionary
crypto_dictionary = {}

#we read the local .json file
filename = 'currency_limits_25032021.json'

#we create a function to convert json to dictionary
def __convert_to_dict(filename,dictionary): #convert object to dictionary
    """ from a .json filename, we return a dictionary """
    try:
        with open(filename) as json_file:
            data = json.load(json_file)
        dictionary.update(data)
    except JSONDecodeError:
        print ('JSON decode failed')

#We run our json file through the converter
__convert_to_dict(filename,crypto_dictionary)

#Our global crypto_dictionary is now updated.

Sample of dictionary output

{'e': 'currency_limits', 'ok': 'ok', 'data': {'pairs': [{'symbol1': 'BTC', 'symbol2': 'USD', 'pricePrecision': 1, 'minLotSize': 0.0004, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '3500', 'maxPrice': '350000'}, {'symbol1': 'ETH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.012, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '26.41', 'maxPrice': '10000'}, {'symbol1': 'BCH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.0

We see that is it not exactly the same as our json file
That is because it’s now a data dictionary
It contains single quotes instead of double quotes

Data dictionary = key-value pair

We use that property to get the things we need.

# Here we need the third key, i.e. data
# We just reference it from our global dictionary
data_dict = crypto_dictionary['data']
print (data_dict)

Sample Output of data_dict

{'pairs': [{'symbol1': 'BTC', 'symbol2': 'USD', 'pricePrecision': 1, 'minLotSize': 0.0004, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '3500', 'maxPrice': '350000'}, {'symbol1': 'ETH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.012, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '26.41', 'maxPrice': '10000'}, {'symbol1': 'BCH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.02, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '43.40', 'maxPrice': '8192'}, {'symbol1': 'DASH', 'symbol2': 'USD', 'pricePrecision': 3, 'minLotSize': 0

‘pairs’ is another data dictionary

How do i know ? It starts with curly braces.

From ‘pairs’ I require the value(s).

So we reference it further.

pairs = data_dict['pairs']
print (pairs)

Sample output of values of pairs list

[{'symbol1': 'BTC', 'symbol2': 'USD', 'pricePrecision': 1, 'minLotSize': 0.0004, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '3500', 'maxPrice': '350000'}, {'symbol1': 'ETH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.012, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '26.41', 'maxPrice': '10000'}, {'symbol1': 'BCH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.02, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '43.40', 'maxPrice': '8192'}, {'symbol1': 'DASH', 'symbol2': 'USD', 'pricePrecision': 3, 'minLotSize': 0.065, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '12.98', 'maxPrice': '4096'}, {'symbol1': 'LTC', 'symbol2': 'USD', 'pricePrecision': 3, 'minLotSize': 0.08, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '7.73', 'maxPrice': '2048'}, {'symbol1': 'XRP', 'symbol2': 'USD', 'pricePrecision': 5, 'minLotSize': 11, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '0.0347', 'maxPrice': '10'}, {'symbol1': 'XLM', 'symbol2': 'USD', 'pricePrecision': 5, 'minLotSize': 32, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '0.002', 'maxPrice': '10'},

The values of pairs is a list
Why ? if you look upwards, you will see pairs starts with a square bracket`

If you don’t believe me try:

print (type(pairs))
#it will return <class 'list'>

Pairs values: list –> referenced by index

A list as opposed to data dictionaries does not contain key-value pairs
It is made up of indexes
So we read it as an index

size = len(pairs)
print(size)
#size is 190

#we now loop through it
#Remember, indexes always start with zero, so we go from 0 to 190
for i in range(0, size):
    print (pairs[i])

Sample output of values contents

{'symbol1': 'BTC', 'symbol2': 'USD', 'pricePrecision': 1, 'minLotSize': 0.0004, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '3500', 'maxPrice': '350000'}
{'symbol1': 'ETH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.012, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '26.41', 'maxPrice': '10000'}
{'symbol1': 'BCH', 'symbol2': 'USD', 'pricePrecision': 2, 'minLotSize': 0.02, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '43.40', 'maxPrice': '8192'}
{'symbol1': 'DASH', 'symbol2': 'USD', 'pricePrecision': 3, 'minLotSize': 0.065, 'minLotSizeS2': 10, 'maxLotSize': None, 'minPrice': '12.98', 'maxPrice': '4096'}

Now that’s more like it!
We now have a clean dictionary

Read from dat dictionary !

Oh yeah, job just got easier now.
Now, we just need to read some cryptos from that dictionary

#Say we are looking for BTT in particular
#we now loop through it
for i in range(0, size):
    #print (pairs[i])
    crypto = pairs[i]['symbol1']
    market = pairs[i]['symbol2']
    maxprice = pairs[i]['maxPrice']
    if ('BTT' in crypto):
        print (crypto,market,maxprice)

Sample Output

BTT USD 50
BTT EUR 50
BTT BTC 0.0001

Full code

\ Codarren /

Credits

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python data structures

Written on March 25, 2021