Python货币转换器 - 如何处理金额为空

Question

我用 Python/Flask 构建了一个非常简单的货币转换器。我正在使用一个名为forex-python 的库。一切正常，但是当用户将“金额”留空时应用程序崩溃，并且我收到 Python 错误ValueError: could not convert string to float:

我有try.. except 用于ValueError 和TypeError，但它们不起作用。我猜，当用户将“金额”留空时，它会被视为字符串，python 无法将其转换为float

那么我该如何优雅地处理这个问题呢？我只是想将用户重定向到'/' 并向他们显示一条消息。

代码如下：

@app.route('/results', methods=['POST'])
def process():
    conv_from = request.form['conv_from']
    conv_to = request.form['conv_to']
    amount = float(request.form['amount'])
    
    rates = CurrencyRates()
    codes = CurrencyCodes()
    
    try:
        results = round(rates.convert(conv_from, conv_to, amount), 2)
        symbol = codes.get_symbol(conv_to)
        return render_template("/results.html", conv_from=conv_from, conv_to=conv_to, amount=amount, results=results, symbol=symbol)
    except RatesNotAvailableError:
        flash("Please enter a valid currency")
        return redirect('/')
    except (ValueError, TypeError):
        flash("Oops something went wrong")
        return redirect('/')

Answer 1

一个简单的if 语句来检查字符串是否为空就足够了：

@app.route('/results', methods=['POST'])
def process():
    conv_from = request.form['conv_from']
    conv_to = request.form['conv_to']
    if request.form['amount'] == "":
        print("Enter a valid amount")
        return False
    else:
        amount = float(request.form['amount'])
    
    rates = CurrencyRates()
    codes = CurrencyCodes()
    
    try:
        results = round(rates.convert(conv_from, conv_to, amount), 2)
        symbol = codes.get_symbol(conv_to)
        return render_template("/results.html", conv_from=conv_from, conv_to=conv_to, amount=amount, results=results, symbol=symbol)
    except RatesNotAvailableError:
        flash("Please enter a valid currency")
        return redirect('/')
    except (ValueError, TypeError):
        flash("Oops something went wrong")
        return redirect('/')

但是，这只检查字符串是否为空。如果我尝试输入 5 USD 但输入 5xyz 将无法处理。在这种情况下，像这样的 try/catch 块也可以工作。

@app.route('/results', methods=['POST'])
def process():
    conv_from = request.form['conv_from']
    conv_to = request.form['conv_to']
    try:
        amount = float(request.form['amount'])
    except:
        print("Not a valid amount")
    rates = CurrencyRates()
    codes = CurrencyCodes()
    try:
        results = round(rates.convert(conv_from, conv_to, amount), 2)
        symbol = codes.get_symbol(conv_to)
        return render_template("/results.html", conv_from=conv_from, conv_to=conv_to, amount=amount, results=results, symbol=symbol)
    except RatesNotAvailableError:
        flash("Please enter a valid currency")
        return redirect('/')
    except (ValueError, TypeError):
        flash("Oops something went wrong")
        return redirect('/')

Answer 2

您没有在 try/except 块中进行投射。只需更改amount 变量的位置（您使用float 方法对其进行转换的位置），使其位于try/except 块中，并且应该处理异常。

所以解决方法是：

@app.route('/results', methods=['POST'])
def process():
    conv_from = request.form['conv_from']
    conv_to = request.form['conv_to']
    
    rates = CurrencyRates()
    codes = CurrencyCodes()
    
    try:
        amount = float(request.form['amount'])
        results = round(rates.convert(conv_from, conv_to, amount), 2)
        symbol = codes.get_symbol(conv_to)
        return render_template("/results.html", conv_from=conv_from, conv_to=conv_to, amount=amount, results=results, symbol=symbol)
    except RatesNotAvailableError:
        flash("Please enter a valid currency")
        return redirect('/')
    except ValueError:
        flash("Invalid amount provided!")
        return redirect('/')
    except TypeError:
        flash("Oops something went wrong")
        return redirect('/')

Answer 3

我认为这将是最干净的解决方案，如果您愿意，您也可以将 request.form.get() 用于您的其他 request.form 变量。

如果指定的键不存在或变量类型与request.form.get() 中指定的type 不匹配，则request.form.get() 返回None。

Python 代码：

@app.route('/results', methods=['POST'])
def process():
    conv_from = request.form['conv_from']
    conv_to = request.form['conv_to']
    amount = request.form.get('amount', type=float)

    if amount is None:
        flash('Please enter a valid amount!')
        return redirect('/')
    
    rates = CurrencyRates()
    codes = CurrencyCodes()
    
    try:
        results = round(rates.convert(conv_from, conv_to, amount), 2)
        symbol = codes.get_symbol(conv_to)
        return render_template("/results.html", conv_from=conv_from, conv_to=conv_to, amount=amount, results=results, symbol=symbol)
    except RatesNotAvailableError:
        flash("Please enter a valid currency")
        return redirect('/')
    except (ValueError, TypeError):
        flash("Oops something went wrong")
        return redirect('/')