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1. Load the data from currency.txt to use as the currency string which will form part of the rest url.
2. Load the data from crypto.txt to populate the crypto combo box.
3. Get the desired cryptocurrency to be used in the cryptocurrency part of the rest url.

In the previous article, we have hardcoded both the cryptocurrency symbol and the currency symbol string into the rest url but in this chapter, we will read those symbols from a file instead. The entire steps of this revised program are as follows:

Load the data from crypto.txt to populate the crypto combo box when a user open up that application.

BTC
ETH
XRP
LTC
BCH
BNB
USDT
EOS
BSV
XLM
TRX
DASH

# read the crypto.txt file then populate the crypto combo box
curr = tuple() # the tuple which will be populated by cryptocurrencies
with open('crypto.txt') as fp:
    for currency in fp.readlines():
        curr += (currency[:-1],)
crypto['values'] = curr
crypto.current(0)

When the user presses the load button, the program will load the currency.txt file then read those currency symbols that will form a string as a part of the rest url.

EUR
JPY
GBP
USD
AUD

 # read the currency file
    c_string = ''
    with open('currency.txt') as fp:
        for currency in fp.readlines():
            c_string += currency[:-1] + ","
    c_string = c_string[:-1]

Finally get the selected cryptocurrency symbol from the crypto combo box to create the full rest url.

base_crypto = crypto.get()  # get the desired crypto currency
    try:
        url = "https://min-api.cryptocompare.com/data/price" #url for API call
        data = {'fsym' : base_crypto, 'tsyms':c_string}
        r = requests.get(url, params=data)
        exchange_rate_s = json.loads(json.dumps(r.json()))

    except:
        print("An exception occurred")

When the program gets the returned data it will populate the currency combo box as well as showing the cryptocurrency/currency exchange rate on the display panel.

import json
from tkinter import *
import tkinter.ttk as tk
import requests

win = Tk() # Create tk instance
win.title("Crypto Calculator") # Add a title
win.resizable(0, 0) # Disable resizing the GUI
win.configure(background='white') # change window background color

selectorFrame = Frame(win, background="white") # create top frame to hold search button and combobox
selectorFrame.pack(anchor = "nw", pady = 2, padx=10)
currency_label = Label(selectorFrame, text = "Select crypto / currency pair :", background="white")
currency_label.pack(anchor="w")

# Create a combo box for crypto currency
select_currency = StringVar() # create a string variable
crypto = tk.Combobox(selectorFrame, textvariable=select_currency)
crypto.pack(side = LEFT, padx=3)

s = StringVar() # create string variable
# create currency frame and text widget to display the incoming exchange rate data
currencyFrame = Frame(win)
currencyFrame.pack(side=TOP)
currency = Label(currencyFrame)
currency.pack()
text_widget = Text(currency, fg='white', background='black')
text_widget.pack()
s.set("Click the find button below to load the crypto currency - currency exchange rate")
text_widget.insert(END, s.get())

buttonFrame = Frame(win) # create a bottom frame to hold the load button
buttonFrame.pack(side = BOTTOM, fill=X, pady = 6)

# read the data from crypto.txt file then populate the crypto combo box
curr = tuple() # the tuple which will be populated by cryptocurrencies
with open('crypto.txt') as fp:
    for currency in fp.readlines():
        curr += (currency[:-1],)
crypto['values'] = curr
crypto.current(0)

def search_currency(): # search currency pair
    pass #for future use

action_search = tk.Button(selectorFrame, text="Search", command=search_currency) # button used to search the currency pair within the text widget
action_search.pack(side=LEFT)

# Create currency combo box
base_currency = StringVar() # create a string variable
based = tk.Combobox(selectorFrame, textvariable=base_currency)
based.pack(side = LEFT, padx=3)

def get_exchange_rate(): # this method will display the incoming exchange rate data after the api called

    global exchange_rate
    global base_crypto

    # read the currency file
    c_string = ''
    with open('currency.txt') as fp:
        for currency in fp.readlines():
            c_string += currency[:-1] + ","
    c_string = c_string[:-1]

    base_crypto = crypto.get()  # get the desired crypto currency
    try:
        url = "https://min-api.cryptocompare.com/data/price" #url for API call
        data = {'fsym' : base_crypto, 'tsyms':c_string}
        r = requests.get(url, params=data)
        exchange_rate_s = json.loads(json.dumps(r.json()))

    except:
        print("An exception occurred")

    curr1 = tuple() # the tuple which will be populated by currency
    sell_buy = ''

    for key, value in exchange_rate_s.items():  # populate exchange rate string and the currency tuple
        sell_buy += base_crypto + ":" + key + "  " + str(value) + "\n"
        curr1 += (key,)

    # fill up combo boxes for both currency and cryptocurrency
    based['values'] = curr1
    based.current(0)

    text_widget.delete('1.0', END)  # clear all those previous text first
    s.set(sell_buy)
    text_widget.insert(INSERT, s.get())  # populate the text widget with new exchange rate data

action_vid = tk.Button(buttonFrame, text="Load", command=get_exchange_rate) # button used to load the exchange rate of currency pairs
action_vid.pack()

win.iconbitmap(r'ico.ico')
win.mainloop()

The program above looks little bit messy but don’t worry because we will tidy up that program in near future.

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