Python try-except Tutorial: Mastering Error Handling
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Errors are inevitable in programming. But with Python’s try-except blocks, you can gracefully handle exceptions and make your programs more robust, user-friendly, and crash-resistant.
This guide explains:
-
What exceptions are
-
How
try-exceptworks -
Common exception types
-
Advanced usage (
else,finally) -
Real-world examples
-
Tips and common pitfalls
What Is an Exception?
An exception is an error that occurs during the execution of a program, disrupting its normal flow.
Example:
print(10 / 0)
Output:
ZeroDivisionError: division by zero
This stops the program. But what if we could handle it smoothly?
Basic Syntax of try-except
try:
# Code that might throw an error
except SomeException:
# Code to run if an error occurs
Example:
try:
result = 10 / 0
except ZeroDivisionError:
print("You can't divide by zero!")
Output:
You can't divide by zero!
Catching Multiple Exceptions
You can handle multiple specific exceptions:
try:
value = int("abc")
except ValueError:
print("Invalid input: not an integer")
Or handle several at once:
try:
risky_code()
except (ValueError, ZeroDivisionError):
print("Something went wrong with input or math.")
Catching All Exceptions (Use with Caution)
try:
unknown_function()
except Exception as e:
print(f"An error occurred: {e}")
-
✅ Good for logging or debugging
-
⚠️ Not recommended for silent failure or production masking
✅ Using else with try
The else block runs only if no exception was raised.
try:
number = int("42")
except ValueError:
print("Conversion failed")
else:
print("Conversion successful:", number)
Using finally for Cleanup
The finally block always executes, whether or not an exception occurred. It’s useful for resource cleanup like closing files or database connections.
try:
file = open("data.txt", "r")
content = file.read()
except FileNotFoundError:
print("File not found!")
finally:
print("Closing file (if open)")
if 'file' in locals():
file.close()
Common Python Exceptions
| Exception | Raised When... |
|---|---|
ZeroDivisionError |
You divide by zero |
ValueError |
A function gets an argument of the right type but wrong value |
TypeError |
Wrong data type used |
IndexError |
List index out of range |
KeyError |
Dictionary key not found |
FileNotFoundError |
File operation fails because the file doesn't exist |
AttributeError |
You call an attribute that doesn’t exist |
Real-World Example: Safe Input and Division
def safe_divide():
try:
a = int(input("Enter numerator: "))
b = int(input("Enter denominator: "))
result = a / b
except ValueError:
print("Please enter valid integers.")
except ZeroDivisionError:
print("Denominator cannot be zero.")
else:
print(f"Result: {result}")
finally:
print("Operation complete.")
safe_divide()
⚠️ Common Pitfalls
| Pitfall | Explanation | Solution |
|---|---|---|
| Catching everything blindly | Masks bugs | Catch specific exceptions where possible |
Silent except: blocks |
Fail silently | Always log or inform the user |
Not using finally for cleanup |
May leave open resources | Use finally to release files, connections, etc. |
Too much logic in try block |
Hard to debug | Keep try block small and focused |
Tips
✅ Use try-except to handle expected errors (e.g., user input, file access)
✅ Always catch specific exceptions first, then general ones
✅ Log errors during development or in production environments
✅ Use else for code that should only run if no error occurred
✅ Use finally for guaranteed clean-up, even if an exception occurs
Complete Code Example
def process_file(filename):
try:
file = open(filename, "r")
content = file.read()
except FileNotFoundError:
print(f"Error: File '{filename}' does not exist.")
except PermissionError:
print(f"Error: Permission denied for file '{filename}'.")
else:
print("File read successfully:")
print(content)
finally:
if 'file' in locals():
file.close()
print("File closed.")
# Try with an existing and a non-existing file
process_file("example.txt")
Conclusion
Python’s try-except blocks are essential for writing reliable code. By anticipating errors and handling them appropriately, you can make your applications more robust, user-friendly, and maintainable.
Learn to use try, except, else, and finally strategically, and you’ll have the tools to handle almost anything Python throws at you.
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
-
map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
-
reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28
