#!/usr/bin/env python
# coding: utf-8

# # Exceptions
# - dealing with bugs is normal part of programming
# - debugging is a very handy programming skill
# 
# ## category of bugs
# - syntax errors
# - logical/semantic errros
# - runtime errors/exceptions

# ## exceptions
# - when runtime error occurs, it creats an exception object
# - program halts; Python prints out the traceback with error message
# - https://docs.python.org/3/tutorial/errors.html

# In[1]:


print(55/0)


# In[2]:


alist = []
print(alist[0])


# In[3]:


atup = ('a', 'b', 'c')
atup[0] = 'A'


# - each exception has two parts- Name: description

# ## catching exceptions
# - use try and except blocks
# - try statement has several separate clauses/parts
# <pre>
#     try:
#         # statement(s) thay may potentially throw(s) exception
#     except ExceptionName1:
#         # catch specific exception ExceptionName1
#         # statement(s) to handle the exception
#     [except ExceptionName2 as err:
#         # statements
#     ]
#     [except:
#         # catch any error not caught by previous except blocks
#     ]
#     [else:
#         # follows all except clause
#         # executes if try clause does NOT raise an exception
#     ]
#     [finally:
#         # clean-up actions that must be executed under all circumstances; 
#         # exectued on the way out when try block is left via a break, continue, or return statement
#     ]
# </pre>
# - <em>[ ] optional </em> 

# ### example 1

# In[6]:


try:
    x = int(input("Enter dividend: "))
    y = int(input("Enter divisor: "))
    quotient = x/y
    remainder = x%y
except ZeroDivisionError as ex:
    print('Exception occured:', ex)
    print('arguments:', ex.args)
except:
    print('Some exception occured...')
else:
    print("quotient=", quotient)
    print("remainder=", remainder)
finally:
    print("executing finally clause")


# In[ ]:





# ### example 2
# - input validation

# In[7]:


while True:
    try:
        x = int(input("Please enter a number: "))
        break
    except ValueError:
        print("Oops! That was not a valid number. Try again...")


# ## raising exceptions
#  - raise statement allows programer to throw their own exceptions

# ### example 1

# In[8]:


raise NameError("MyException")


# In[9]:


try:
    raise NameError('My Exception')
except NameError:
    print('An exception flew by...')
    raise


# ## user-defined exceptions
# - one can define their own exceptions and raise them as needed
# - should typically derive from the Exception class, either directly or indirectly
# 
# ### example 1

# In[12]:


class InputError(Exception):
    """
    Exception raised for errors in the input.
    
    Attributes:
    expression -- input expression in which the error occured
    message -- explaination of the error
    """
    def __init__(self, expression, message):
        self.expression = expression
        self.message = message
    


# In[13]:


help(InputError)


# In[14]:


def getInteger():
    x = input('Enter an integer number: ')
    if not x.isdigit():
        raise InputError(x, 'That is not an integer!')
    return int(x)


# In[15]:


x = getInteger()
print(x)


# In[ ]: