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

# # [Exceptions](https://docs.python.org/3/library/exceptions.html#concrete-exceptions)
# When something goes wrong an exception is raised. For example, if you try to divide by zero, `ZeroDivisionError` is raised or if you try to access a nonexistent key in a dictionary, `KeyError` is raised.
# 
# 

# In[ ]:


empty_dict = {}
# empty_dict['key']  # Uncomment to see the traceback


# ## `try-except` structure 
# If you know that a block of code can fail in some manner, you can use `try-except` structure to handle potential exceptions in a desired way.

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# Let's try to open a file that does not exist
file_name = "not_existing.txt"

try:
    with open(file_name) as my_file:
        print("File is successfully open")

except FileNotFoundError as e:
    print(f"Uups, file: {file_name} not found")
    print(f"Exception: {e} was raised")


# If you don't know the type of exceptions that a code block can possibly raise, you can use `Exception` which catches all exceptions. In addition, you can have multiple `except` statements.

# In[ ]:


def calculate_division(var1, var2):
    result = 0

    try:
        result = var1 / var2
    except ZeroDivisionError as ex1:
        print("Can't divide by zero")
    except Exception as ex2:
        print(f"Exception: {ex2}")

    return result


result1 = calculate_division(3, 3)
print(f"result1: {result1}")

result2 = calculate_division(3, "3")
print(f"result2: {result2}")

result3 = calculate_division(3, 0)
print(f"result3: {result3}")


# `try-except` can be also in outer scope:

# In[ ]:


def calculate_division(var1, var2):
    return var1 / var2


try:
    result = calculate_division(3, "3")
except Exception as e:
    print(e)


# ## Creating your custom exceptions
# In your own applications, you can use custom exceptions for signaling users about errors which occur during your application run time.  

# In[ ]:


import math


# Define your own exception
class NegativeNumbersNotSupported(Exception):
    pass


# Dummy example how to use your custom exception
def secret_calculation(number1, number2):
    if number1 < 0 or number2 < 0:
        msg = f"Negative number in at least one of the parameters: {number1}, {number2}"
        raise NegativeNumbersNotSupported(msg)

    return math.sqrt(number1) + math.sqrt(number2)


# Uncomment to see the traceback
# result = secret_calculation(-1, 1)