錯誤處理入門

Python 函式入門

Hugo Bowne-Anderson

Instructor

`float()` 函式

2016-08-09 上午 9:38:27 的螢幕截圖-4885.png

傳入不正確的引數

float(2)

2.0

float('2.3')

2.3

float('hello')

<hr />---------------------------------------------------------------
ValueError                       Traceback (most recent call last)
<ipython-input-3-d0ce8bccc8b2> in <module>()
<hr />-> 1 float('hi')
ValueError: could not convert string to float: 'hello'

傳入有效引數

def sqrt(x):
    """Returns the square root of a number."""
    return x ** (0.5)
sqrt(4)

2.0

sqrt(10)

3.1622776601683795

傳入無效引數

sqrt('hello')

------------------------------------------------------------------
TypeError                        Traceback (most recent call last)
<ipython-input-4-cfb99c64761f> in <module>()
----> 1 sqrt('hello')
<ipython-input-1-939b1a60b413> in sqrt(x)
      1 def sqrt(x):
----> 2     return x**(0.5)
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'float'

錯誤與例外

例外：執行期間擷取
用 try-except 捕捉例外
- 先執行 try 後的程式碼
- 若發生例外，執行 except 後的程式碼

錯誤與例外

def sqrt(x):
    """Returns the square root of a number."""
    try:
        return x ** 0.5
    except:
        print('x must be an int or float')


sqrt(4)

2.0

sqrt(10.0)

3.1622776601683795

sqrt('hi')

x must be an int or float

錯誤與例外

def sqrt(x):
    """Returns the square root of a number."""
    try:
        return x ** 0.5
    except TypeError:
        print('x must be an int or float')

2016-08-09 上午 10:04:32 的螢幕截圖-4904.png

錯誤與例外

sqrt(-9)

(1.8369701987210297e-16+3j)

def sqrt(x):
    """Returns the square root of a number."""
    if x < 0:
        raise ValueError('x must be non-negative')
    try:
        return x ** 0.5
    except TypeError:
        print('x must be an int or float')

錯誤與例外

sqrt(-2)

-----------------------------------------------------------------
ValueError                      Traceback (most recent call last)
<ipython-input-2-4cf32322fa95> in <module>()
----> 1 sqrt(-2)
<ipython-input-1-a7b8126942e3> in sqrt(x)
      1 def sqrt(x):
      2     if x < 0:
----> 3         raise ValueError('x must be non-negative')
      4     try:
      5         return x**(0.5)
ValueError: x must be non-negative

一起來練習吧！

Python 函式入門