Python File Write Tutorial: How to Write to Files in Python
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Python makes it easy to create and write to files using the built-in open() function and file methods like .write() and .writelines(). Whether you're saving user input, logging events, or exporting data, writing to files is a key programming task.
In this article, you'll learn:
-
How to write to files in Python
-
The difference between write modes (
w,a,x) -
Using
.write()and.writelines() -
Best practices with
with open(...) -
A full working example
-
Tips and common mistakes
Opening a File for Writing
To write to a file, use the open() function with the correct file mode:
file = open("filename.txt", "w") # 'w' for write
Common Write Modes
| Mode | Description |
|---|---|
'w' |
Write mode: overwrites the file if it exists |
'a' |
Append mode: adds to the end of the file |
'x' |
Create mode: creates a new file, errors if it exists |
Use
'w'to start fresh,'a'to keep existing content,'x'to ensure a file is created only if it doesn't exist.
✍️ Writing with .write()
The .write() method writes a single string to a file.
with open("example.txt", "w") as f:
f.write("Hello, world!\n")
f.write("Second line of text.\n")
Each call to .write() adds the string exactly as given. To write new lines, include \n.
Writing Multiple Lines with .writelines()
The .writelines() method writes a list of strings to the file without adding newline characters automatically.
lines = ["First line\n", "Second line\n", "Third line\n"]
with open("example.txt", "w") as f:
f.writelines(lines)
❗ You must add
\nmanually to each string if you want line breaks.
✅ Best Practice: Use with to Handle Files
The with statement ensures the file is closed properly after writing, even if an error occurs.
Example:
with open("data.txt", "w") as f:
f.write("Using with statement is safer.")
This is cleaner and avoids the need for f.close().
Append to a File with 'a' Mode
To keep existing data and add new content:
with open("log.txt", "a") as f:
f.write("New log entry.\n")
This adds to the end of the file without removing existing content.
Complete Example: Save a To-Do List
def save_todo_list(filename, tasks):
with open(filename, "w") as f:
for task in tasks:
f.write(task + "\n")
def add_task(filename, task):
with open(filename, "a") as f:
f.write(task + "\n")
def read_todo_list(filename):
with open(filename, "r") as f:
print("To-Do List:")
print(f.read())
# Usage
tasks = ["Buy groceries", "Finish Python tutorial", "Call Alice"]
save_todo_list("todo.txt", tasks)
add_task("todo.txt", "Walk the dog")
read_todo_list("todo.txt")
Output:
To-Do List:
Buy groceries
Finish Python tutorial
Call Alice
Walk the dog
⚠️ Common Mistakes and How to Avoid Them
| Mistake | Problem | Solution |
|---|---|---|
Not using with |
File may stay open | Always use with open(...) |
Forgetting \n |
All content on one line | Add \n to each line |
Using 'w' instead of 'a' |
File gets erased | Use 'a' for appending |
| Writing non-string data | TypeError | Use str() or f-strings to convert data |
Pro Tips
-
Use
"utf-8"encoding to support special characters:open("file.txt", "w", encoding="utf-8") -
Use
.join()and.writelines()to write large lists efficiently -
Use
'x'mode to prevent accidentally overwriting files -
Always test file-writing scripts on sample data before writing to important files
Summary
| Task | Example |
|---|---|
| Write to new file | open("file.txt", "w") |
| Append to file | open("file.txt", "a") |
| Write a single string | f.write("text") |
| Write multiple lines | f.writelines(["line1\n", "line2\n"]) |
| Safely write and close file | with open(...) as f: |
Final Thoughts
Writing files in Python is easy and powerful. With the right file mode and structure, you can create logs, reports, user data files, and much more. Just remember to use with, manage your newline characters, and choose the correct mode (w, a, or x) depending on your goal.
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
