# Exception Handling in Python

# When a program encounters an error condition, instead of crashing
# it can "throw and exception".  Exceptions are better than having the
# program crash, or (worst case) continue to run erroneously.


A = [2,3,5]

try:
  x = int(input("enter integer:")) #could raise error if string is not a number
  print(1/(x-2)) # could raise division by zero error
  if (x<0): raise Exception("don't be negative") # user-raised error
  print(A[9])  # raises index out of range error
except ZeroDivisionError:    print("Error: you can't divide by zero!")
except IndexError:    print("Error: your array isn't that big")
except ValueError:    x = int(input("enter a number, not something else please:"))
except Exception as exp:    print("Exception raised:",exp) # prints exception's message
except:    print("Unexpected error")
    
# Run this program. At least it will throw the IndexError because of A[9].
# Enter 2 for x to get the divison by zero error, enter "abc" to get the
# 'ValueError' and enter -1 to get the user generated exception.

# Note that the last except clause catches all other errors.

## Exceptions should only be used to address situations that cannot be
#  predicted by the algorithm.  In general, you should not raise an
#  exception if it is something that can be handled using conventional
#  methods, such as an if-else.


# The following functions illustrates the correct use of exceptions:

# The following function computes n! (5! = 5*4*3*2*1):
def factorial(n):
    if (n<0): raise Exception("factorial is undefined for negative numbers")
    ax = 1
    while n>1:
        ax = ax*n
        n -= 1
    return ax
#factorial

def smallest(A): # smallest value in A
    if (len(A)==0): raise Exception("function undefined for empty arrays")
    ax = A[0]
    i = 1
    while i<len(A):
        if A[i]<ax: ax = A[i]
        i += 1
    return ax
#smallest