Python File Handling: A Complete Tutorial for Beginners
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File handling is a crucial skill for any Python programmer. It allows you to read from and write to files, automate workflows, process logs, store user data, and much more. Python provides simple yet powerful ways to interact with files using built-in functions like open(), read(), write(), and close().
In this tutorial, you’ll learn:
-
What file handling is
-
How to open, read, write, and close files
-
File modes in Python (
r,w,a, etc.) -
Using the
withstatement -
Handling text and binary files
-
Tips and common pitfalls
What Is File Handling?
File handling means working with files — creating, opening, reading, writing, appending, and closing them. In Python, this is typically done using the built-in open() function and file object methods.
Opening a File
The open() function is used to open a file:
file = open("example.txt", "r")
Syntax:
open(file, mode='r', buffering=-1, encoding=None, errors=None)
Common File Modes:
| Mode | Description |
|---|---|
'r' |
Read (default). File must exist. |
'w' |
Write. Overwrites file or creates a new one. |
'a' |
Append. Adds to the end of file. |
'x' |
Exclusive creation. Fails if file exists. |
'b' |
Binary mode (e.g., 'rb', 'wb') |
't' |
Text mode (default) |
Reading from a File
.read(): Read entire content
with open("example.txt", "r") as file:
content = file.read()
print(content)
.readline(): Read line-by-line
with open("example.txt", "r") as file:
line = file.readline()
while line:
print(line.strip())
line = file.readline()
.readlines(): Read all lines as a list
with open("example.txt", "r") as file:
lines = file.readlines()
print(lines)
✍️ Writing to a File
.write(): Write string to file
with open("output.txt", "w") as file:
file.write("Hello, Python!\n")
file.write("File handling is easy.")
⚠️
wmode will overwrite the file if it already exists.
.writelines(): Write a list of strings
lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open("output.txt", "w") as file:
file.writelines(lines)
➕ Appending to a File
To add content to an existing file without deleting its contents, use 'a' mode:
with open("output.txt", "a") as file:
file.write("New appended line.\n")
✅ Using the with Statement (Best Practice)
with open("example.txt", "r") as file:
data = file.read()
print(data)
Benefits of with:
-
Automatically closes the file
-
Prevents file corruption
-
Cleaner and safer
Working with Binary Files
To handle binary files like images or videos:
Reading binary file:
with open("image.png", "rb") as file:
content = file.read()
Writing binary file:
with open("copy.png", "wb") as file:
file.write(content)
Handling File Exceptions
try:
with open("important.txt", "r") as file:
print(file.read())
except FileNotFoundError:
print("File does not exist.")
except IOError:
print("An I/O error occurred.")
Complete Example: Copying Text from One File to Another
def copy_file(source, destination):
try:
with open(source, "r") as src, open(destination, "w") as dest:
for line in src:
dest.write(line)
print("File copied successfully.")
except FileNotFoundError:
print("Source file not found.")
except Exception as e:
print(f"Error: {e}")
# Example usage
copy_file("input.txt", "output.txt")
⚠️ Common Pitfalls and How to Avoid Them
| Pitfall | Solution |
|---|---|
| Forgetting to close files | Use with open(...) |
| File not found | Use try-except or check with os.path.exists() |
Using wrong mode (r when file doesn’t exist) |
Use w, a, or check before opening |
| Writing without newline | Use \n at the end of each line |
Tips for Effective File Handling
-
Always use
withto manage file context -
For large files, process line-by-line instead of using
.read() -
Use
'b'mode for binary files (e.g., images, PDFs) -
Handle exceptions to avoid crashing your program
-
Use
os.path.exists()orpathlib.Path.exists()to verify files
Summary Table
| Task | Method |
|---|---|
| Open a file | open("file.txt", "r") |
| Read file | .read(), .readline(), .readlines() |
| Write to file | .write(), .writelines() |
| Append to file | open("file.txt", "a") |
| Read/write binary | Use 'rb' / 'wb' modes |
| Best practice | with open(...) as file: |
Final Thoughts
Python file handling is simple, readable, and powerful. Whether you're dealing with logs, user data, configuration files, or large datasets, understanding how to work with files effectively is an essential skill. Always follow best practices, handle exceptions gracefully, and ensure data integrity by properly closing files.
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
