while True:
try:
x = int(input("Please enter a number: "))
break
except ValueError:
print("Oops! That was no valid number. Try again ")

except (RuntimeError, TypeError, NameError):
pass

try:
 raise KeyboardInterrupt
 finanlly:
 print("dooo")

# ---------------------------------------------------------------------#
# 異常處理
# ---------------------------------------------------------------------#
while True:
 try:
 x = int(input("Please enter a number: "))
 break
 except ValueError:
 print("Oops! That was no valid number. Try again ")

# ---------------------------------------------------------------------#
# 拋出異常
# ---------------------------------------------------------------------#
"""
try:
 raise NameError('HiThere')
except NameError:
 print('An exception flew by!')
 raise
"""

# ---------------------------------------------------------------------#
# 用戶自定義異常
# ---------------------------------------------------------------------#
class MyError(Exception): # 繼承自Exception
 def __init__(self, value): # 構(gòu)造函數(shù)重寫
 self.value = value

 def __str__(self):
 return repr(self.value)
try:
 raise MyError(2*2) # 拋出異常
except MyError as e:
 print('My exception occurred, value:', e.value)
# 當(dāng)創(chuàng)建一個模塊有可能拋出多種不同的異常時(shí)，
# 一種通常的做法是為這個包建立一個基礎(chǔ)異常類，
# 然后基于這個基礎(chǔ)類為不同的錯誤情況創(chuàng)建不同的子類
class Error(Exception):
 """Base class for exceptions in this module."""
 pass
class InputError(Error):
 """Exception raised for errors in the input.
 Attributes:
 expression -- input expression in which the error occurred
 message -- explanation of the error
 """
 def __init__(self, expression, message):
 self.expression = expression
 self.message = message
class TransitionError(Error):
 """Raised when an operation attempts a state transition that's not
 allowed.

 Attributes:
 previous -- state at beginning of transition
 next -- attempted new state
 message -- explanation of why the specific transition is not allowed
 """

 def __init__(self, previous, next1, message):
 self.previous = previous
 self.next = next1
 self.message = message


try:
 raise InputError(2*2, 45) # 拋出異常
except InputError: # 處理異常
 print('My exception occurred')

# ---------------------------------------------------------------------#
# 定義清理行為
# ---------------------------------------------------------------------#

def divide(x, y):
 try:
 result = x / y
 except ZeroDivisionError:
 print("division by zero!")
 else: # 沒有異常的時(shí)執(zhí)行
 print("result is", result)
 finally: # 無論在任何情況下都會執(zhí)行的清理行為
 print("executing finally clause")


# 一個異常在 try 子句里（或者在 except 和 else 子句里）被拋出，
# 而又沒有任何的 except 把它截住，那么這個異常會在 finally 子句執(zhí)行后再次被拋出
# divide("2", "1") #從測試代碼