Python currency converter Decimal Float Mismatch Error

Question

I'm trying to build a very simple currency converter with Python/Flask. I'm using a library called forex-python . When I try this in the command line using ipython. Everything works great:

In [1]: from forex_python.converter import CurrencyRates
In [2]: c = CurrencyRates()
In [3]: c.convert('USD', 'EUR', 10)
Out[3]: 8.259002313

Great, But when I try this by running a flask server and doing it in the browser. it doesn't work. My form in index:html looks like this:

<form action="/results" method="post">
    <p>Converting from <input type="text" name="convert_from" placeholder="USD"></p>
    <p>Converting to <input type="text" name="convert_to" placeholder="EUR"></p>
    <p>Amount <input type="text" name="amount" placeholder="10"></p>
    <p><button>Send</button></p>
</form>

And in app.py, the /results route looks like this:

@app.route('/results', methods=['POST'])
def process():
    convert_from = request.form['convert_from']
    convert_to = request.form['convert_to']
    amount = request.form['amount']

c = CurrencyRates()
results = c.convert(convert_from, convert_to, amount)
return render_template("/results.html", results=results)

And then the results.html page is simply:

<p>
    The converted amount is {{ results }}
</p>

When I run this in the browser, I fill the form and hit submit to go to /results. I get the following error:

forex_python.converter.DecimalFloatMismatchError
forex_python.converter.DecimalFloatMismatchError: convert requires amount parameter is of type Decimal when force_decimal=True 

This is odd, because I'm not using force_decimal=true. So why is this error happening? And why does it work fine in ipython, but not in the browser?

Answer 1

Your form-POST json values will be of type string since inputs give strings

@app.route('/results', methods=['POST'])
def process():
    convert_from = float(request.form['convert_from'])
    convert_to = float(request.form['convert_to'])
    amount = float(request.form['amount'])

    c = CurrencyRates()
    results = c.convert(convert_from, convert_to, amount)
    return render_template("/results.html", results=results)

float is a builtin to convert other compatible data-types to float(Decimals) and I would recommend changing the input type to number(U still need float) so that the user cant cause errors with the float function