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EXCEPTION HANDLING IN PYTHON 2023 When an exception occurs, it causes the program to stop executing and hand over to the calling process. If the exception is not handled in time, it can cause your code to fail.

Exception vs syntax error vs logic error EXCEPTION HANDLING IN PYTHON 2023 methood?

A syntax error is when the interpreter encounters an incorrect statement. It simply means that python doesn’t know how to execute this pattern EXCEPTION HANDLING IN PYTHON 2023:

In the above example, we found a syntax error due to more parentheses.

A logic error is an error when the mathematical logic or reasoning of an expression or statement is incorrect. Due to this error we will not get the desired result.

If you want to get addition and use subtraction logic, it will be a logic error.

Exceptions are runtime errors. They occur in some specific cases.


How to throw an exception EXCEPTION HANDLING IN PYTHON 2023?

In some specific cases, we can declare an exception ourselves. Stops current code execution and throws an exception EXCEPTION HANDLING IN PYTHON 2023.

Syntax to throw an exception:

We can also throw an exception by assigning a variable or defining a function.


By defining a function

4. How to handle exception: Try and Except block

An exception must be handled as soon as we see it, otherwise the program may crash.

For this we use a try and catch block EXCEPTION HANDLING IN PYTHON 2023.

In the try block we put the code that causes the exception, while in the exception block we give the response to any exception.

We use a try and exception block to handle this TypeError exception:

This time output will be EXCEPTION HANDLING IN PYTHON 2023:

5. Usage Finally

As mentioned above, we have seen when an exception occurs how we can handle it using a try and catch block.

In some cases, we want some code to run under any condition (It doesn’t matter if an exception occurs or not).

To finally understand the concept, let’s look at this example:

In the code above, we took a string and used a try, then in addition to handling the exception, we finally used a finally block. The code always executes eventually EXCEPTION HANDLING IN PYTHON 2023.

As we can see, the code where the string contains the value “abc” will eventually convert to “abc changes to python”.

So far, the error messages haven’t been more than mentioned, but if you’ve tried the examples, you’ve probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions.

8.1. Syntax errors
Syntax errors, also known as parsing errors, are perhaps the most common kind of complaint you’ll get when you’re still learning Python EXCEPTION HANDLING IN PYTHON 2023:

while True print (“Hello world”)
File “<stdin>”, line 1
while True print (“Hello world”)
SyntaxError: invalid syntax
The parser repeats the problematic line and displays a small “arrow” pointing to the earliest point on the line where the error was detected. The error is caused (or at least detected) by the token before the arrow: in the example, the error is detected in the print() function because it is missing a colon (‘:’) before it. The file name and line number are printed so you know where to look in case the input comes from a script EXCEPTION HANDLING IN PYTHON 2023.

8.2. Exceptions
Even if a statement or expression is syntactically correct, it may cause an error when you try to execute it. Errors encountered during execution are called exceptions EXCEPTION HANDLING IN PYTHON 2023, and they are not necessarily fatal: you will soon learn how to handle them in Python programs. However, most exceptions are not handled by the programs and result in error messages as shown here:

10* (1/0)
Backtracking (last last call):
File “<stdin>”, line 1, in <module>
ZeroDivisionError: division by zero
4 + spam*3
Backtracking (last last call):
File “<stdin>”, line 1, in <module>
NameError: name ‘spam’ is undefined
‘2’ + 2
Backtracking (last last call):
File “<stdin>”, line 1, in <module>
TypeError: can only concatenate str (not “int”) to str
The last line of the error message indicates what happened. Exceptions have different types, and the type is printed as part of the message: the types in the example are ZeroDivisionError, NameError, and TypeError. The string printed as the exception type is the name of the built-in exception that occurred. This applies to all built-in exceptions, but may not apply to user-defined exceptions (although it is a useful convention). Standard exception names are built-in identifiers (not reserved keywords) EXCEPTION HANDLING IN PYTHON 2023.

The rest of the line provides details based on the type of exception and what caused it.

The previous part of the error message shows the context where the exception occurred, in the form of a stack trace back. It generally contains a stack traceback with a list of source lines; however, it will not display lines read from standard input EXCEPTION HANDLING IN PYTHON 2023.


Built-in Exceptions lists the built-in exceptions and their meaning.

8.3. Exception handling
It is possible to write programs that handle selected exceptions. Look at the following example, which prompts the user for input until a valid integer is entered, but allows the user to abort the program (using Control-C or whatever the operating system supports); note that a user-generated interrupt is signaled by throwing a KeyboardInterrupt exception.

The try command works as follows.

First, the try clause (the statement(s) between the try and exception keywords) is executed.

If no exception occurs, the except clause is skipped and execution of the try statement is completed.

If an exception occurs during the execution of the try clause, the rest of the clause is skipped. If its type matches an exception named after the exception keyword, the exception clause is executed and execution continues after the try/except block EXCEPTION HANDLING IN PYTHON 2023.

If an exception occurs that does not match the exception specified in the exception clause, it is passed to the outer try statements; if no handler is found, it is an unhandled exception and execution stops with a message as above.

A try statement can have more than one exception clause that specifies handlers for different exceptions. At most one handler will be executed. Handlers only handle exceptions that occur in the corresponding try clause, not in other handlers of the same try statement. An except clause can name multiple exceptions as tuples in parentheses, for example:

… except (RuntimeError, TypeError, NameError):
… fold
A class in an exception clause is compatible with an exception if it is the same class or its base class (but not vice versa—an exception clause specifying a derived class is not compatible with the base class). For example, the following code prints B, C, D in that order:

Note that if the except clauses were reversed (with exception B first), it would print B, B, B — the first matching except clause would run EXCEPTION HANDLING IN PYTHON 2023.

When an exception occurs, it can have associated values, also known as exception arguments. The presence and types of arguments depend on the exception type.

An exception clause can specify a variable after the exception name. A variable is bound to an exception instance, which usually has an args attribute that stores the arguments. For convenience, they define built-in exception types
The exception’s __str__() output is printed as the last part (“detail”) of the message for unhandled exceptions.

BaseException is the common base class of all exceptions. One of its subclasses, Exception, is the base class for all soft exceptions. Exceptions that are not subclasses of the Exception class are not usually handled because they are used to indicate that the program should terminate. They include SystemExit, which is called by sys.exit(), and KeyboardInterrupt, which is called when the user wishes to interrupt the program.

Exception can be used as a wildcard to catch (almost) everything. However, it is good practice to be as specific as possible about the types of exceptions we intend to handle and to allow propagation of any unexpected exceptions.

The most common way to handle an exception is to print or log the exception and then re-throw it (allowing the caller to also handle the exception) EXCEPTION HANDLING IN PYTHON 2023:

When a Python program encounters an error, it stops the execution of the rest of the program. A Python error can be either an error in the syntax of an expression or a Python exception. Let’s see what kind of exception it is. In this tutorial we will also see the difference between a syntax error and an exception. Then we will learn about try and exception blocks and how to raise exceptions and make assertions. After that we will see the list of Python exceptions.

What is an exception?

An exception in Python is an incident that happens during the execution of a program and causes a disruption in the regular execution of the program’s statements. When Python code encounters a condition it cannot handle, it throws an exception. An object in Python that describes an error is called an exception.

When Python code throws an exception, it has two options: handle the exception immediately, or stop and exit.

Exceptions versus syntax errors
Syntax errors occur when the interpreter identifies a statement that contains an error. Consider the following scenario:
Play video

An exception is an error that occurs during program execution. Exceptions are known to non-programmers as instances that do not conform to a general rule. The name “exception” in computer science also has this meaning: It means that a problem (exception) does not occur often, so an exception is an “exception to the rule”. Exception handling is a construct in some programming languages ​​that automatically handles or deals with errors. Many programming languages ​​like C++, Objective-C, PHP, Java, Ruby, Python and many others have built-in support for exception handling.

Error handling is generally handled by saving the state of execution at the time the error occurred and interrupting the normal flow of the program to execute a special function or piece of code known as an exception handler. Depending on the type of error (“division by zero”, “error opening file”, etc.) that occurred, the error handler can “fix” the problem and the program can then continue with the previously saved data.

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Exception Handling in Python
Exception handling in Python is very similar to Java. The code that hides the risk of an exception is placed inside a try block. While in Java, exceptions are caught with catch clauses, in Python we have statements preceded by the “except” keyword. It is possible to create “tailor-made” exceptions: Using the raise command, it is possible to force the occurrence of a specified exception.

Let’s look at a simple example. Assuming we want to ask the user to enter an integer. If we use input(), the input will be a string that we need to cast to an integer. If the input is not a valid integer, we generate (raise) a ValueError. We will demonstrate this in the following interactive session:

n = int(input(“Please enter a number:”))
Using exception handling, we can write robust code to read an integer from input:

while true:
n = input(“Please enter an integer: “)
n = int(n)
except ValueError:
print(“No valid integer! Please try again…”)
print(“Great, you have successfully entered an integer!”)
It is a loop that only breaks if a valid integer has been entered. A while loop is entered. The code in the try clause will be executed statement by statement. If no exception occurs during execution, execution reaches a break statement and the while loop is exited. If an exception occurs, i.e. when casting n, the rest of the try block is skipped and the exception clause is executed. The error declared, in our case ValueError, must match one of the names after the exception. In our example, only one, i.e. “ValueError:”. After the text of the print command is printed, the execution performs another loop. It starts with new input().

We could turn the above code into a function that can be used to create a reliable input EXCEPTION HANDLING IN PYTHON 2023.


def int_input(prompt):
while true:
age = int(input(prompt))
return age
except ValueError like e:
print(“Invalid integer! Try again”)
We use this with our dog’s age example from the Conditional Statements chapter.

def dog2human_age(dog_age):
human_age = -1
if dog_age < 0:
human_age = -1
elif dog_age == 0:
human_age = 0
elif dog_age == 1:
human_age = 14
elif dog_age == 2:
human_age = 22
human_age = 22 + (dog’s age -2) * 5
return human_age
age = int_input(“Your dog’s age?”)
print(“Age of dog: “, dog2human_age(age))
Not a valid integer! try it again
Not a valid integer! try it again
Dog’s age: 37
Multiple out clauses
A try statement can have more than one exception clause for different exceptions. But at most one except clause will be executed.

Our next example shows a try clause in which we open a file for reading, read a line from that file, and convert that line to an integer. There are at least two possible exceptions:

error IOError
In case we have another unnamed exception clause for an unexpected error EXCEPTION HANDLING IN PYTHON 2023:

import sys

f = open(‘integers.txt’)
s = f.readline()
i = int(s.strip())
except IOError as e:
errno, strerror = e.args
print(“I/O Error({0}): {1}”.format(errno,strerror))
# e can be printed directly without using .args:
# print(s)
except ValueError:
print(“There is no valid integer in the line.”)
except for:
print(“Unexpected error:”, sys.exc_info()[0])
I/O error(2): No such file or directory
The IOError handling in the previous example is of particular interest. The exception clause for IOError specifies the variable “e” after the exception name (IOError). The variable “e” is bound to the exception instance with the arguments stored in instance.args. If we call the above script with a non-existent file, we get the message:

I/O error(2): No such file or directory

And if the integers.txt file is not readable, i.e. if we don’t have permission to read it, we get the following message:

I/O error(13): Permission denied  EXCEPTION HANDLING IN PYTHON 2023

The except clause can name more than one exception in a tuple of error names, as seen in the following example:

Exceptions are errors that are detected during execution. Exceptions are thrown whenever there is an error in the program EXCEPTION HANDLING IN PYTHON 2023.

If these exceptions are not handled, it puts the program in a halted state. Exception handling is necessary to prevent sudden program termination. This article will further explain exception handling in Python.

This article will introduce you to what exceptions are and why it is necessary to handle them in the first place.
We will learn about when exceptions are thrown, how they can be thrown manually, and how to handle exceptions in python EXCEPTION HANDLING IN PYTHON 2023.
Writing code to solve or automate some big problems is a pretty powerful thing, isn’t it? But as Peter Parker says, ‘with great power comes great responsibility’. This is actually true even when writing code! During the execution of our code, some events may occur that disrupt the normal flow of your code. These events are errors, and once they occur, the python interpreter is in a situation it can’t handle, so it throws an exception.

In python, an exception is a class that represents an error. If these exceptions are not handled, our applications or programs will go into a failed state. As developers, we definitely have the authority to write code and solve problems, but it is our responsibility to handle these exceptions that may occur and break the code flow.

Let’s see in this article how these exceptions can be handled, but first let’s look at an example that will introduce you to an exception  EXCEPTION HANDLING IN PYTHON 2023:

a = 10
b = 0
c = b/a
print (c)

Backtracking (last last call):
File “”, line 3, in <module>
c = a/b
ZeroDivisionError: division by zero
Above is an example of what we call an unhandled exception. On line 3, the code went into a stopped state because it is an unhandled exception. To avoid such stop states, let’s see how to handle exceptions/errors.

What is exception handling in Python EXCEPTION HANDLING IN PYTHON 2023?
Exceptions may be unexpected, or in some cases, the developer may expect some code flow disruption due to an exception that may occur in a particular scenario. Either way, it needs to be handled.

Python, like any other programming language, provides us with provisions for handling exceptions. And that is to block the try & except. The try block allows us to write code that is prone to exceptions or errors. If any exception occurs inside the try block, the exception block is triggered where you can handle the exception, because now the code will not go into the stopped state, but the control will go into the exception block where it can be handled manually EXCEPTION HANDLING IN PYTHON 2023.

Any critical block of code can be written in the try clause. Once an expected or unexpected exception is thrown in this try, it can be handled inside the except clause (this “except” clause is triggered when the exception is thrown inside the “try”) because this except block detects any exception thrown in the try block. By default, except detects all exception types because all built-in exceptions in python are inherited from the regular Exception class.

The basic syntax is as follows EXCEPTION HANDLING IN PYTHON 2023:

# Some code
except for:
# Done if an error occurs in the try block
# Handle the exception here

Try and besides go hand in hand ie the syntax is to write and use both. Just try typing or an exception will throw an error EXCEPTION HANDLING IN PYTHON 2023.

Let’s look at an example where we divide two numbers. The Python interpreter throws an exception when we try to divide the number by 0. When this happens, we can do our own action on it in the exception clause EXCEPTION HANDLING IN PYTHON 2023.

def divisionNos(a, b):
return a/b

DivisionNose(10, 0)
except for:
print(‘an exception occurred’)

some exception occurred
But how do we know exactly what error the python interpreter read EXCEPTION HANDLING IN PYTHON 2023?

When the python interpreter throws an exception, it is in the form of an object that contains information about the exception type and message. Every exception type in python also inherits from the Exception base class.

def divisionNos(a, b):
return a/b
DivisionNose(10, 0)
# Any exception thrown by the python interpreter is inherited by the ‘Exception’ base class, so any exception thrown in the try block will be caught and collected further in the exception block for processing.
except for an exception like e:
print(e) # as e is an object of type Exception, print here to see what message it contains.
print (e.__class__)
division by zero
<class ‘ZeroDivisionError’>
In the above code, we have used the Exception class with the exception statement. It is used with the as keyword. This object will contain the reason for the exception and we print it to find out what the reason is inside this exception object EXCEPTION HANDLING IN PYTHON 2023.

Common Exceptions in Python
Before proceeding further, we need to understand what are some common exceptions that python throws. All built-in exceptions in python are inherited from the common class ‘Exception’. Some of the common built-in exceptions are EXCEPTION HANDLING IN PYTHON 2023:


In topics of protection, as in subjects of faith – all people chooses for himself the most that he WHILE LOOP IN PYTHON.


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