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Errors and Exceptions in Python

  • Difficulty Level : Medium
  • Last Updated : 22 Oct, 2021

Errors are the problems in a program due to which the program will stop the execution. On the other hand, exceptions are raised when some internal events occur which changes the normal flow of the program. 
Two types of Error occurs in python. 
 

  1. Syntax errors
  2. Logical errors (Exceptions) 
     

 

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Syntax errors

When the proper syntax of the language is not followed then a syntax error is thrown.
Example 
 



Python3




# initialize the amount variable
amount = 10000
  
# check that You are eligible to
#  purchase Dsa Self Paced or not
if(amount>2999)
    print("You are eligible to purchase Dsa Self Paced")
     


Output:
 

It returns a syntax error message because after the if statement a colon: is missing. We can fix this by writing the correct syntax.
 

logical errors(Exception)

When in the runtime an error that occurs after passing the syntax test is called exception or logical type. For example, when we divide any number by zero then the ZeroDivisionError exception is raised, or when we import a module that does not exist then ImportError is raised.
Example 1: 
 

Python3




# initialize the amount variable
marks = 10000
  
# perform division with 0
a = marks / 0
print(a)


Output:
 

In the above example the ZeroDivisionError as we are trying to divide a number by 0.
Example 2: When indentation is not correct. 
 

Python3




if(a<3):
print("gfg")


Output:
 

Some of the common built-in exceptions are other than above mention exceptions are:
 

 

Exception Description
IndexError When the wrong index of a list is retrieved.
AssertionError It occurs when the assert statement fails
AttributeError It occurs when an attribute assignment is failed.
ImportError It occurs when an imported module is not found.
KeyError It occurs when the key of the dictionary is not found.
NameError It occurs when the variable is not defined.
MemoryError It occurs when a program runs out of memory.
TypeError It occurs when a function and operation are applied in an incorrect type.

Note: For more information, refer to Built-in Exceptions in Python
 

Error Handling

When an error and an exception are raised then we handle that with the help of the Handling method.
 

  • Handling Exceptions with Try/Except/Finally 
    We can handle errors by the Try/Except/Finally method. we write unsafe code in the try, fall back code in except and final code in finally block.
    Example 
     

Python3




# put unsafe operation in try block
try:
     print("code start")
          
     # unsafe operation perform
     print(1 / 0)
  
# if error occur the it goes in except block
except:
     print("an error occurs")
  
# final code in finally block
finally:
     print("GeeksForGeeks")


  • Output: 
     
code start
an error occurs
GeeksForGeeks
  •  
  • Raising exceptions for a predefined condition 
    When we want to code for the limitation of certain conditions then we can raise an exception. 
    Example 
     

Python3




# try for unsafe code
try:
    amount = 1999
    if amount < 2999:
          
        # raise the ValueError
        raise ValueError("please add money in your account")
    else:
        print("You are eligible to purchase DSA Self Paced course")
              
# if false then raise the value error
except ValueError as e:
        print(e)


  • Output: 
     
please add money in your account



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