Python continue on error

In this Python tutorial, we will discuss the Python While loop continue. Here we will also cover the below examples:

• Python while loop continue break
• Python while loop exception continue
• Python nested while loop continue
• Python while true loop continue
• While loop continue python example
• Python continue while loop after exception
• Python try except continue while loop
• Python while loop break and continue

• Let us see how to use the continue statement in the While loop in Python.
• Continue is used to skip the part of the loop. This statement executes the loop to continue the next iteration.
• In python, the continue statement always returns and moves the control back to the top of the while loop.

Example:

Let’s take an example and check how to use the continue statement in the while loop

new_var = 8
while new_var >0:
    new_var=new_var-1
    if new_var==2:
        continue
    print(new_var)
print("loop end")

In the above code, we will first initialize a variable with 8 and check whether 8 is greater than 0. Here you can see it is true so I will go for a decrement statement that 8-1 and it will display the variable value as 7. it will check whether a variable is equal to 2. In the above code, you will check that it is not equal to the variable and it will print the value 7.

Here is the output of the following above code

Another example is to check how to use the continue statement in the while loop in Python.

Example:

z = 8
while z > 1:
    z -= 2
    if z == 3:
        continue
    print(z)
print('Loop terminate:')

Here is the screenshot of the following given code

Read: Python For Loop

Python while loop continue break

• In python, the break and continue statements are jump statements. The break statement is used to terminate the loop while in the case of the continue statement it is used to continue the next iterative in the loop.
• In the break statement, the control is transfer outside the loop while in the case of continue statement the control remains in the same loop.

Example:

while True:
    result = input('enter a for the loop: ')
    if result == 'a':
        break
print('exit loop')

a = 0
while a <= 8 :
    a += 1
    if a % 4 == 1 :
        continue
    print(a)

In the above code, we will create a while loop and print the result 2 to 8, But when we get an odd number in the while loop, we will continue the next loop. While in the case of the break statement example we will give the condition that if the user takes the input as ‘a’ it will exit the loop.

Output

Read: Python While Loop

Python while loop exception continue

• Let us see how to use the exception method in the while loop continue statement in Python.
• An exception is an event that occurs normally during the execution of a programm.
• If a statement is systematically correct then it executes the programm. Exception means error detection during execution.
• In this example, we can easily use the try-except block to execute the code. Try is basically the keyword that is used to keep the code segments While in the case of except it is the segment that is actually used to handle the exception.

Example:

while True:
    try:
        b = int(input("enter a value: "))
        break
    except  ValueError:
        print("Value is not valid")

Screenshot of the given code

Read: Python While loop condition

Python nested while loop continue

• Let us see how to use nested while loop in Python.
• In this example, we will use the continue statement in the structure of the within while loop based on some important conditions.

Example:

Let’s take an example and check how to use nested while loop in Python

c = 2
while c < 4 :
    d = 1
    while d < 10 :
        if d % 2 == 1 :
            d += 1
            continue
        print(c*d, end=" ")
        d += 1
    print()
    c += 1

Here is the execution of the following given code

This is how to use nested while loop in python.

Python while true loop continue

In Python, the while loop starts if the given condition evaluates to true. If the break keyword is found in any missing syntax during the execution of the loop, the loop ends immediately.

Example:

while True:
    output = int(input("Enter the value: "))
    if output % 2 != 0:
        print("Number is odd")
        break
    
    print("Number is even")

In the above code, we will create a while loop and print the result whether it is an even number or not, when we get an odd number in the while loop, we will continue the next loop. In this example we take a user input when the user enters the value it will check the condition if it is divide by 2 then the number is even otherwise odd.

Here is the implementation of the following given code

Read: Python while loop multiple conditions

While loop continue Python example

• Here we can see how to use the continue statement while loop.
• In this example first, we will take a variable and assign them a value. Now when n is 4 the continue statement will execute that iteration. Thus the 4 value is not printed and execution returns to the beginning of the loop.

Example:

Let’s take an example and check how to use the continue statement in the while loop

l = 6
while l > 0:
    l -= 1
    if l == 4:
        continue
    print(l)
print('Loop terminate')

Output

Another example to check how to apply the continue statement in the while loop

Example:

t = 8                  
while 8 > 0:              
   print ('New value :', t)
   t = t-1
   if t == 4:
      break

print ("Loop end")

Here is the output of the program

Read: Python dictionary length

Python try except continue while loop

• Here we can check how to apply the try-except method in the continue while loop.
• In this example, I want to convert the input value inside a while loop to an int. In this case, if the value is not an integer it will display an error and continue with the loop.

Example:

m=0
new_var=0
l = input("Enter the value.")
while l!=str("done"):
     try:
          l=float(l)
     except:
          print ("Not a valid number")
          continue
     m=m+1
     new_var = l + new_var      
     l= input("Enter the value.")
new_avg=new_var/m
print (new_var, "g", m, "g", new_avg)

Here is the implementation of the following given code

Python while loop break and continue

• In Python, there are two statements that can easily handle the situation and control the flow of a loop.
• The break statement executes the current loop. This statement will execute the innermost loop and can be used in both cases while and for loop.
• The continue statement always returns the control to the top of the while loop. This statement does not execute but continues on the next iteration item.

Example:

Let’s take an example and check how to use the break and continue statement in while loop

k = 8                    
while k > 0:              
   print ('New value :', k)
   k = k -1
   if k == 4:
      break

print ("loop terminate")

b = 0
while b <= 8 :
    b += 1
    if b % 4 == 1 :
        continue
    print(b)
  

Output:

This is how to use the break and continue statement in while loop

You may also like reading the following articles.

• Registration form in Python using Tkinter
• Extract text from PDF Python
• Python loop through a list
• For loop vs while loop in Python
• Python for loop index

In this Python tutorial, we have discussed the Python While loop continue. Here we have also covered the following examples:

• Python while loop continue break
• Python while loop exception continue
• Python nested while loop continue
• Python while true loop continue
• While loop continue python example
• Python continue while loop after exception
• Python try except continue while loop
• Python while loop break and continue

In Python programming, exception handling allows a programmer to enable flow control. And it has no. of built-in exceptions to catch errors in case your code breaks. Using try-except is the most common and natural way of handling unexpected errors along with many more exception handling constructs. In this tutorial, you’ll get to explore some of the best techniques to use try-except in Python.

Error Handling or Exception Handling in Python can be enforced by setting up exceptions. Using a try block, you can implement an exception and handle the error inside an except block. Whenever the code breaks inside a try block, the regular code flow will stop and the control will get switched to the except block for handling the error.

Why use Try-Except/Try-Except-else Clause? With the help of try-except and try-except-else, you can avoid many unknown problems that could arise from your code. For example, the Python code using LBYL (Look before you leap) style can lead to race conditions. Here, the try-except clause can come to rescue you. Also, there are cases where your code depends critically on some information which could get outdated till the time you receive it. For example, the code making calls to os.path.exists or Queue.full may fail as these functions might return data that become stale by the time you use it. The wiser choice here would be to follow the try-except-else style in your code to manage the above cases more reliably.

Raising exceptions is also permissible in Python. It means you can throw or raise an exception whenever it is needed. You can do it simply by calling [raise Exception(‘Test error!’)] from your code. Once raised, the exception will stop the current execution as usual and will go further up in the call stack until handled.

Why use Exceptions? They not only help solve popular problems like race conditions but are also very useful in controlling errors in areas like loops, file handling, database communication, network access and so on.

Hence, we’ll cover broader problems and provide solutions in this post. Please note that exception handling is an art which brings you immense powers to write robust and quality code. So, brace to read some keynotes on exceptions along with the best ways to handle them.

Must Read – Everything You Should Know About Python Copy File [Python File I/O].

Python: Tips to Use Try-Except, Try-Except-Else, and More

• How to handle an arbitrary exception
• Catch multiple exceptions in one except block
• Handling multiple exceptions with one except block
• Re-raising exceptions in Python
• When to use the else clause
• Make use of [finally clause]
• Use the As keyword to catch specific exception types
• Best practice for manually raising exceptions
• How to skip through errors and continue execution
• Most common exception errors in Python
• Examples of most common exceptions in Python

1. How to handle an arbitrary exception

Sometimes, you may need a way to allow any arbitrary exception and also want to be able to display the error or exception message.

It is easily achievable using the Python exceptions. Check the below code. While testing, you can place the code inside the try block in the below example.

try:
    #your code
except Exception as ex:
    print(ex)

Back to top

2. Catch multiple exceptions in one except block

You can catch multiple exceptions in a single except block. See the below example.

except (Exception1, Exception2) as e:
    pass

Please note that you can separate the exceptions from the variable with a comma which is applicable in Python 2.6/2.7. But you can’t do it in Python 3. So, you should prefer to use the [as] keyword.

Back to top

3. Handling multiple exceptions with one except block

There are many ways to handle multiple exceptions. The first of them requires placing all the exceptions which are likely to occur in the form of a tuple. Please see from below.

try:
    file = open('input-file', 'open mode')
except (IOError, EOFError) as e:
    print("Testing multiple exceptions. {}".format(e.args[-1]))

The next method is to handle each exception in a dedicated except block. You can add as many except blocks as needed. See the below example.

try:
    file = open('input-file', 'open mode')
except EOFError as ex:
    print("Caught the EOF error.")
    raise ex
except IOError as e:
    print("Caught the I/O error.")
    raise ex

The last but not the least is to use the except without mentioning any exception attribute.

try:
    file = open('input-file', 'open mode')
except:
    # In case of any unhandled error, throw it away
    raise

This method can be useful if you don’t have any clue about the exception possibly thrown by your program.

Back to top

4. Re-raising exceptions in Python

Exceptions once raised keep moving up to the calling methods until handled. Though you can add an except clause which could just have a [raise] call without any argument. It’ll result in reraising the exception.

See the below example code.

try:
    # Intentionally raise an exception.
    raise Exception('I learn Python!')
except:
    print("Entered in except.")
    # Re-raise the exception.
    raise

Output:

Entered in except.
Traceback (most recent call last):
  File "python", line 3, in <module>
Exception: I learn Python!

Back to top

5. When to use the else clause

Use an else clause right after the try-except block. The else clause will get hit only if no exception is thrown. The else statement should always precede the except blocks.

In else blocks, you can add code which you wish to run when no errors occurred.

See the below example. In this sample, you can see a while loop running infinitely. The code is asking for user input and then parsing it using the built-in [int()] function. If the user enters a zero value, then the except block will get hit. Otherwise, the code will flow through the else block.

while True:
    # Enter integer value from the console.
    x = int(input())

    # Divide 1 by x to test error cases
    try:
        result = 1 / x
    except:
        print("Error case")
        exit(0)
    else:
        print("Pass case")
        exit(1)

Back to top

6. Make use of [finally clause]

If you have a code which you want to run in all situations, then write it inside the [finally block]. Python will always run the instructions coded in the [finally block]. It is the most common way of doing clean up tasks. You can also make sure the clean up gets through.

An error is caught by the try clause. After the code in the except block gets executed, the instructions in the [finally clause] would run.

Please note that a [finally block] will ALWAYS run, even if you’ve returned ahead of it.

See the below example.

try:
    # Intentionally raise an error.
    x = 1 / 0
except:
    # Except clause:
    print("Error occurred")
finally:
    # Finally clause:
    print("The [finally clause] is hit")

Output:

Error occurred
The [finally clause] is hit

Back to top

7. Use the As keyword to catch specific exception types

With the help of as <identifier>, you can create a new object. And you can also the exception object. Here, the below example, we are creating the IOError object and then using it within the clause.

try:
    # Intentionally raise an error.
    f = open("no-file")
except IOError as err:
    # Creating IOError instance for book keeping.
    print("Error:", err)
    print("Code:", err.errno)

Output:

('Error:', IOError(2, 'No such file or directory'))
('Code:', 2)

Back to top

8. Best practice for manually raising exceptions

Avoid raising generic exceptions because if you do so, then all other more specific exceptions have to be caught also. Hence, the best practice is to raise the most specific exception close to your problem.

Bad example.

def bad_exception():
    try:
        raise ValueError('Intentional - do not want this to get caught')
        raise Exception('Exception to be handled')
    except Exception as error:
        print('Inside the except block: ' + repr(error))
        
bad_exception()

Output:

Inside the except block: ValueError('Intentional - do not want this to get caught',)

Best Practice:

Here, we are raising a specific type of exception, not a generic one. And we are also using the args option to print the incorrect arguments if there is any. Let’s see the below example.

try:
    raise ValueError('Testing exceptions: The input is in incorrect order', 'one', 'two', 'four') 
except ValueError as err:
    print(err.args)

Output:

('Testing exceptions: The input is in incorrect order', 'one', 'two', 'four')

Back to top

9. How to skip through errors and continue execution

Ideally, you shouldn’t be doing this. But if you still want to do, then follow the below code to check out the right approach.

try:
    assert False
except AssertionError:
    pass
print('Welcome to Prometheus!!!')

Output:

Welcome to Prometheus!!!

Back to top

Now, have a look at some of the most common Python exceptions and their examples.

Most common exception errors

• IOError – It occurs on errors like a file fails to open.
• ImportError – If a python module can’t be loaded or located.
• ValueError – It occurs if a function gets an argument of right type but an inappropriate value.
• KeyboardInterrupt – It gets hit when the user enters the interrupt key (i.e. Control-C or Del key)
• EOFError – It gets raised if the input functions (input()/raw_input()) hit an end-of-file condition (EOF) but without reading any data.

Back to top

Examples of most common exceptions

except IOError:
print('Error occurred while opening the file.')

except ValueError:
print('Non-numeric input detected.')

except ImportError:
print('Unable to locate the module.')

except EOFError:
print('Identified EOF error.')

except KeyboardInterrupt:
print('Wrong keyboard input.')

except:
print('An error occurred.')

Back to top

while programming, errors are bound to happen. It’s a fact which no one can ignore. And there could be many reasons for errors like bad user input, insufficient file permission, the unavailability of a network resource, insufficient memory or most likely the programmer’s mistake.

Anyways, all of this can be handled if your code use exception handling and implement it with constructs like try-except, or tr-except-else, try-except-finally. Hope, you would have enjoyed reading the above tutorial.

If you liked the post, then please don’t miss to share it with friends and on social media (facebook/twitter).

Best,
TechBeamers.

1. Use the try-except Statement With continue to Skip Iterations in a Python Loop
2. Use the if-else Statement With continue to Skip Iterations in a Python Loop

This article explains different ways to skip the specific iterations of a loop in Python.

Sometimes, we have to deal with the requirements of performing some tasks repeatedly while skipping a few of them in between. For example, when you are running a loop and want to skip the part of that iteration that can throw an exception.

Use the try-except Statement With continue to Skip Iterations in a Python Loop

In Python, exceptions can be easily handled through a try-except statement. If you think that you may come across some exceptions during loop iterations, due to which the execution of the loop may stop, then you can use this statement.

List_A=[25, 30, 100, 600]
List_B= [5, 10, 0, 30]
Result=[]
for i, dividend in enumerate(List_A):
    try:
      # perform the task
      Result.append(dividend/List_B[i])
    except:
      # handle the exceptions
      continue
print(Result)

In the above code, we have two lists, and we want to divide List_A by List_B element by element.

In Python, when you divide a number by zero, the ZeroDivisionError occurs. Since List_B contains zero as a divisor, division by it will generate this error during loop execution.

So to avoid this error, we use the except block. The exception will be raised when the error occurs, and the except block will be executed.

The continue statement ignores any subsequent statements in the current loop iteration and returns to the top of the loop. This is how you can skip the loop iterations.

The above code generates the following output:

Use the if-else Statement With continue to Skip Iterations in a Python Loop

We can do the same task with an if-else statement and continue.

List_A=[25, 30, 100, 600]
List_B= [5, 10, 0, 30]
Result=[]
for i, dividend in enumerate(List_A):
  if List_B[i]!=0:
    Result.append(dividend/List_B[i])
  else:
    continue
print(Result)

This is a straightforward code. The difference between this solution and the try-except solution is that the former implementation already knows the condition for which the loop execution may get stopped.

Therefore, this condition can be explicitly coded to skip that iteration.

Output:

As a result of the above implementations, you can skip loop iteration on which error/exception may occur without the loop being halted.