How to Handle Errors and Exceptions in Python ?
In this post , we will explore How to Handle Errors and Exceptions in Python. Python errors can be Broadly of two categories -
- Errors
- Exceptions.
x = 1
y = 0
z = x/y
- ValueError: when an argument to a function is the right type but not in the right domain (e.g. an empty string)
- ImportError: raised when some import fails
- IOError: raised when some files not accessible
- SyntaxError - raised when Python code is incorrect.
- KeyError: raised when trying to access a key in a dictionary that does not exist
- TypeError: raised when an argument to a function is not the correct type (e.g. a str instead of float)
1. Single Exception Handling :
The basic practice to handle an Exception scenario is by using a try-except code block. The basic syntax of the try-except block is -
try:
<ANY\_BUSINESS\\MATHEMATICAL\_LOGIC\_CODE >
except <EXCEPTION\_NAME> as error:
print("Exception occured")
2. Multiple Exception Handling :
try:
<ANY\_BUSINESS\\MATHEMATICAL\_LOGIC\_CODE >
except <EXCEPTION\_NAME\_1> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_2> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_3> as error:
print("<ANYTHING\_YOU\_WANT>")
3. Generalized Exception Handling :
If you would like to have a Generalized Handling of Multiple Exceptions together that can be done as shown below. Look at the last code block for Generalized Exception Handling Approach. Note : The Order of the Exception Code Blocks are Very Important . Python follows a Top-Down Approach while executing the Exception Code Block. If Generalized Exception Handling is kept BEFORE any Specific Exception Block Handling (Unlike shown below) , then Python will ALWAYS execute ONLY the Generalized Exception Handling block.
try:
<ANY\_BUSINESS\\MATHEMATICAL\_LOGIC\_CODE >
except <EXCEPTION\_NAME\_1> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_2> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_3> as error:
print("<ANYTHING\_YOU\_WANT>")
except Exception as error:
print(f"An exception occurred {error}")
4. "Try-Finally" Exception Override Handling :
The "finally" block is executed irrespective of any kind of Exceptions . Sometimes a Clean-up or Database_Connection\File-Close activities or operations needs to be carried out MANDATORILY irrespective of Exception or No-Exceptions. Such things can be handled using the "finally" block. See example below -
try:
<ANY\_BUSINESS\\MATHEMATICAL\_LOGIC\_CODE >
except <EXCEPTION\_NAME\_1> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_2> as error:
print("<ANYTHING\_YOU\_WANT>")
except <EXCEPTION\_NAME\_3> as error:
print("<ANYTHING\_YOU\_WANT>")
except Exception as error:
print(f"An exception occurred {error}")
finally:
<Clean-up\_or\_Database\_Connection\\File-Close Activity>
5. "try-finally-else-except" Exception Override Handling :
We can extend the Exception handling process to add some extra - "else" block. The "else" block gets executed ONLY IF No exception gets caught. While the "finally" block gets executed irrespective of anything as explained in Section4.
try:
<DO\_Something>
except <EXCEPTION\_NAME> as error:
print("I print ONLY When this Exception occurs")
else:
print("I Print if No Exception occurs")
finally:
print("I print irrespective of Exception or No Exception")
6. User Defined Exception Handling :
User can create or define their Own Exceptions , based on Specific Business Logic, if the existing In-Bulit Python Exceptions doesn't cover the requirement or you wish to integrate some more sophisticated logging system or further inspect an object. (P.S. - More Details about Custom Exception Handling is our post - How to Code Custom Exception Handling in Python ? ) Let's say the - you have certain Business Logic which Upon not been met , a USER-DEFINED New Exception has to be raised. So first you code the Business Logic as to what EXACTLY is expected. The custom exception class inherits from the base Exception class. The __init__() method is required when defining an Exception class:
<import\_Statements>
import os
import errno
class <Custom\_Exception\_Name>(Exception):
"""Exception raised for errors Custom case.
Attributes:
message -- explain about the error
"""
def \_\_init\_\_(self, message):
# Calling the Base class constructor with the parameters
super().\_\_init\_\_(message)
def <Custom\_Function> ()
if <CHECK\_IF\_BUSINESS\_CRITERIA\_is\_MET>
<NO\_NEED\_TO\_DO\_ANYTHING>
else: ##### DEFINE THE EXCEPTION DETAILS HERE
raise <Custom\_Exception\_Name>(errno.ENOENT, os.strerror(errno.ENOENT))
Custom\_Function()
7. Logging the Exception Handling :
It is also helpful to log the exception message sometimes for subsequent analysis process.
import logging
logTheException = logging.getLogger(\_\_name\_\_)
def start():
try:
<ANY\_BUSINESS\\MATHEMATICAL\_LOGIC\_CODE >
except <EXCEPTION\_NAME\_1> as error:
logTheException .error(error)
raise
- Apache Spark Tricky Interview Questions Part 1
- How To Read Various File Formats in PySpark (Json, Parquet, ORC, Avro) ?
- How To Fix – Indentation Problem in Python ?
- How To Read(Load) Data from Local, HDFS & Amazon S3 in Spark ?
- How To Create A Kerberos Keytab File ?
- How to Create a Multi Node Hadoop\Spark Cluster in Google Cloud(GCP) ?
- How To Install Google Cloud GCP Command Line Utility gcloud ?
- How To Code SparkSQL in PySpark – Examples Part 1
- How To Setup Spark Scala SBT in Eclipse
- How To Read Kafka JSON Data in Spark Structured Streaming
- How to Purge a Running Kafka Topic ?
- How To Fix – Message Out Of Order Issue in Kafka Broker ?
- How To Fix – “Not all brokers have rack information” Error in Kafka ?
- How to Setup a Multi Node Kafka Cluster or Brokers ?