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Error and Exceptions

Error and Exceptions

  • Syntax errors occur when Python can’t interpret our code, since we didn’t follow the correct syntax for Python. These are errors you’re likely to get when you make a typo, or you’re first starting to learn Python.

  • Exceptions occur when unexpected things happen during execution of a program, even if the code is syntactically correct. There are different types of built-in exceptions in Python, and you can see which exception is thrown in the error message.

try statement

We can use try statement to catch exceptions and define how to handle it, the try statement has for parts:

  • try: this is the only mandatory clause in a try statement. this is the first block python will run (and is where we suspect can be and error).
  • except: if Python runs into an exception while running the try block, it will jump to the except block that handle the exception ( they are different type of exception that i will mention down).
  • else: if Python runs into no exception while running the try block, it will run the code in this block after running the try.
  • finally: before Python leave the try block, it will run the code in the finally block.

an example of the simple try will be:

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while True:
    try:
        x = int(input("Enter a number: "))
        break
    except:
        print("Please enter a number")
    finally:
        print("Attempt input")

so, in the previous code if the user enter other value that a valid int the except block will be run and after that the code in finally

now, if the user try to stop the execution using the ctrl + c in the terminal the except block will be run, to avoid this we can select specific exceptions to be capture.

Specifying Exceptions

the exception to handle can be specify in the code, for example:

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try:
    # some code
except valueError:
    #some code

Now, in this case the except block will catch the exception ValueErrror but not other exception. We can catch the exception KeyboardInterrupt at the same time ( this apply to other exception not this two)

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try:
    # some code
except (ValueError, KeyboardInterrupt):
    # some code

in the previous case the exception are going to be handle in the same way, but if we required different response to a different exception, it can be done in the following way:

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try:
    #some code
except ValueError:
    #some code
except KeyboardInterrupt:
    # some code

Accessing Error Messages

Previously we saw how to handle the error, basically how to avoid the program crash when a error appears, but we don't get information about the error, but, there is a way to display this errors, and it is as follow:

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try:
    # some code
except ZeroDivisionError as e:
    #some code
    print("ZeroDivisionErro occurred: {}".format(e))

this would print something like this:

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ZeroDivisionError occurred: integer division or modulo by zero

so in that way you can handle errors, preventing the program for crashing and at the same time get information about the error.

In those case where there are not specific errors to handle, you can use a general form to access to those messages:

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try:
    #some code
except Exception as e:
    #some code
    print("Exception occurred: {} ".format(e))

for more information about exception check this link