# Handling Exceptions In Python Python uses special objects called `exceptions` to handle errors *that arise during a program’s execution* (as opposed to Syntax errors). Therefore whenever an error occurs, Python creates an **exception object** * If we write the code that handles the exception using `try-except` block, the program will continue running. * If we don’t handle the exception, the program will halt and show a `traceback`, which includes a report of the error that was raised. #### Few examples of Exceptions ```python 10 * (1/0) Traceback (most recent call last): File "", line 1, in ZeroDivisionError: division by zero 4 + spam*3 Traceback (most recent call last): File "", line 1, in NameError: name 'spam' is not defined '2' + 2 Traceback (most recent call last): File "", line 1, in TypeError: Can't convert 'int' object to str implicitly ``` `ZeroDivisionError`, `NameError` and `TypeError` in above examples are example of exception objects. ## 1. Handling Exceptions While writing the code, if we know that a specific type of error may occur, we can write a `try- except` block to handle that particular exception . Here is a quick example to deal with `ZeroDivisionError` using `try-except` block ```python try: answer = 5/0 except ZeroDivisionError: print("You can't divide a number with zero") ``` ``` You can't divide a number with zero ``` * The only code that should go inside a `try` block is the code that might cause a specific exception * If the code in a `try` block works, Python skips the `except` block * If the code in the `try` block causes an exception, Python goes to `except` block, *where exception matches the one that was raised*, and runs the code in the `except` block * If more code follows after the `try-except` block, it will be executed as normal because we told Python how to handle the error. ## 2. The else Block Any code that should be executed, *if* the `try` block runs successfully, goes into the `else` block. Example will make the concept clearer ```python try: first_number = input("Enter first number: ") int(first_number) second_number = input("Enter the second number: ") int(second_number) sum = int(first_number) + int(second_number) except ValueError: print("Only numbers are allowed") else: print(f"The sum of {first_number} and {second_number} is {sum}") ``` ``` EXAMPLE 1: Enter first number: 10 Enter the second number: 20 The sum of 10 and 20 is 30 EXAMPLE 2: Enter first number: 10 Enter the second number: twenty Only numbers are allowed ``` * In above example, we asked user to `input` two numbers * then we convert them into integer using `int()` * if user input string, the `int()` function will cause the `ValueError` and the code in `except` block will execute, telling user that only numbers are allowed * however, if the user `input` both numbers, the `else` block will execute ## 3. Analyzing Text (using try-except) In this example, we will combine the concepts learned until now: ```python # writing a function to count words def count_word_instances(file_path, word_to_count): # using try except block to handle FileNoTFoundError try: with open(file_path) as book_object: book_content = book_object.read() except FileNotFoundError: print("Given file path is not correct, please correct it.") else: word_count = book_content.lower().count(word_to_count) words = book_content.split() print(f"The book has approx {len(words)} words") print(f"The word {word_to_count} appered {word_count} times") # providing the path to file file_path_here = "alice_book.txt" # asking user to input the desired word word_to_watch_here = input("What word would you like to search: ") # calling function count_word_instances(file_path_here, word_to_watch_here) ``` ``` What word would you like to search: love The book has approx 124592 words The word love appeared 122 times ``` * rather than separately writing a `try-except-else` block, we wrapped it inside a function * in `try` block, we opened the file and store its content inside the variable `book_content` * if the file doesn’t exist at given path, the `except` block will be executed, telling that the file path is not correct * if the `try` block executes successfully, the `else` block will be executed, telling the number of words in the book and count of user provided keyword in the book * lastly, we call to this function, by giving the filename and words to count * as the file name was correct, Python told us the number of words and count of word provided by the user ## 4. Failing Silently In the previous example, using a custom message in `except` block, we informed our users that file is unavailable. But, if we want, we don’t need to report exception — this behavior is called \*\* failing silently\*\* and program continue on as if nothing happened. To make a program fail silently, we write a `try` block as usual, but explicitly tell Python to do nothing in the `except` block. To do nothing, we will use `pass` statement in `except` block ```python try: answer = 5/0 except ZeroDivisionError: pass ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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