key error python LEARNOVITA

What are Python KeyError Exceptions ? Expert’s Top Picks

Last updated on 27th Oct 2022, Artciles, Blog

About author

Jahir Usain (RPA with Python )

Jahir Usain is a Python developer with 4+ years of experience in Python, NLP, NLTK, and IBM Watson Assistant. His articles help the learners get insights into the domain.

(5.0) | 19578 Ratings 2195
    • In this article you will get
    • Introduction
    • Exceptions versus Syntax Errors
    • Raising an Exception
    • The Assertion Error Exception
    • The try and except Block: The Handling Exceptions
    • Cleaning Up After Using finally
    • Conclusion

Introduction

A Python program are terminates as soon as it encounters an error. In a Python, an error can be a syntax error or exception. In this article, will see what an exception is and how it varies from a syntax error. After that, will learn about raising an exceptions and making assertions. Then, wi,ll finish with a demonstration of a try and except block.

Example for Python Key error

Exceptions versus Syntax Errors

Syntax errors occur when a parser detects an incorrect statement. Observe a following example:

  • >>> print( 0 / 0 ))
  • File “<"stdin">“, line 1
  • print( 0 / 0 ))
  • ^
  • SyntaxError: invalid syntax

The arrow indicates where a parser ran into syntax error. In this example, there was a one bracket too many. Remove it and run a code again:

This time, ran into an exception error. This type of an error occurs whenever syntactically correct a Python code results in an error. The last line of a message indicated what type of an exception error ran into.

Instead of a showing the message exception error, Python details what type of an exception error was encountered. In this case, it was ZeroDivisionError. Python comes with a various built-in exceptions as well as possibility to create a self-defined exceptions.

Raising an Exception

Can use raise to throw exception if a condition occurs. The statement can be a complemented with custom exception.If need to throw an error when a certain condition occurs using raise, and could go about it like this:

  • x = 10
  • if x > 5:
  • raise Exception(‘x should not be exceed 5. The value of a x was: {}’.format(x))
  • When run this code, the output will be a following:
  • Traceback (most recent call last):
  • File “<"input">“, line 4, in <"module">
  • Exception: x should not be exceed 5. The value of a x was: 10

The program comes to be a halt and displays our exception to a screen, offering a clues about what went wrong.

The Assertion Error Exception

Instead of waiting for the program to crash midway, and can also start by making the assertion in Python. Assert that a certain condition is met. If this condition turns out to be a True, then that is excellent! The program can be continue. If condition turns out to be False, can have the program throw the AssertionError exception.

Have a look at a following example, where it is an asserted that a code will be executed on Linux system:

  • import sys
  • assert (‘linux’ in sys.platform), This code runs on a Linux only.

If run this code on a Linux machine, an assertion passes. If were to run this code on Windows machine, the outcome of a assertion would be False .In this example, throwing the AssertionError exception is a last thing that the program will do. The program will come to be halt and will not continue.

Python exceptions

The try and except Block: Handling Exceptions

The try and except block in a Python is used to catch and also handle exceptions. Python executes a code following the try statement as a “normal” part of a program. The code that follows an except statement is a program’s response to any exceptions in preceding try clause.

As saw earlier, when syntactically correct a code runs into an error, Python will throw the exception error.This exception are error will crash the program if it is be unhandled. The except clause a determines how a program responds to an exceptions The linux_interaction() can only run on Linux system. The assert in this function will throw the AssertionError exception if call it on an operating system other then a Linux.

The way handled the error here is by handing out the pass. If were to run this code on the Windows machine,got nothing. The good thing here is that a program did not crash. To this end, can change the pass into the something that would generate informative message, like so:

  • When an exception occurs in the program running this function, the program will be continue as well as inform about the fact that the function call was not be successful.
  • What did not get to see was a type of error that was thrown as a result of a function call. In order to see an exactly what went wrong, and would need to catch error that a function threw.
  • The first message is an AssertionError, informing that the function can only be an executed on a Linux machine. The second message are tells which function was not be executed.
  • In the previous, called a function that are wrote yourself. When executed a function, caught a AssertionError exception and printed it to screen.
  • Can have more than one function call in a try clause and anticipate catching the various exceptions. A thing to note here is that a code in the try clause will stop as soon as exception is encountered.

If a file does not exist, running this code on the Windows machine will output are following:

Function can only run on a Linux systems.

  • Linux linux_interaction() function was not be executed

Inside a try clause, you ran into an exception immediately and did not get to a part where you attempt to open file.log. Here are key takeaways:

  • A try clause is an executed up until the point where a first exception is encountered.
  • Inside a except clause, or the exception handler, find how the program responds to an exception.
  • Can anticipate the multiple exceptions and differentiate how a program should respond to them.
  • Avoid using a bare except clauses.

Cleaning up after using finally

Imagine that always had to implement a some sort of action to clean up after an executing a code. Python enables to do so using a finally clause.Everything in the finally clause will be an executed. It does not matter if can encounter an exception somewhere in a try or else clauses. Running a previous code on a Windows machine.

Conclusion

Raise allows to throw an exception at a any time.Assert enables to verify if a certain condition is met and throw the exception if it isn’t.In a try clause, all statements are executed until a exception is be encountered.Except is used to catch and handle exception(s) that are encountered in a try clause.Else lets code sections that are should run only when no exceptions are be encountered in a try clause.Finally enables to execute sections of code that are should always run, with or without any previously encountered exceptions.

Are you looking training with Right Jobs?

Contact Us

Popular Courses