
Python String Formatting Tutorial: Modern Ways to Format Strings
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String formatting is an essential part of Python that allows you to inject variables into strings, format numbers, align text, and more. Whether you're building a user interface, writing logs, or generating reports, mastering string formatting will make your code more readable and powerful.
This tutorial covers:
-
Different ways to format strings in Python
-
f-strings
,format()
, and%
formatting -
Number formatting
-
Alignment and padding
-
Tips, pitfalls, and a complete example
What is String Formatting?
String formatting lets you dynamically construct strings by inserting variables and controlling how data appears.
For example:
name = "Alice"
print(f"Hello, {name}!")
Output:
Hello, Alice!
Method 1: f-Strings (Python 3.6+)
The f-string (formatted string literal) is the most modern and readable way to format strings.
Syntax:
f"Text {expression}"
Example:
name = "Bob"
age = 30
print(f"{name} is {age} years old.")
Output:
Bob is 30 years old.
You can also use expressions directly:
print(f"Next year, {age + 1} years old.")
Method 2: str.format()
The .format()
method works in Python 2.7+ and 3.x and is very flexible.
Basic Usage:
"{} is {} years old".format("Bob", 30)
Output:
Bob is 30 years old
Using Named Placeholders:
"{name} is {age} years old".format(name="Alice", age=25)
Reordering:
"{1} comes after {0}".format("first", "second")
Method 3: %-formatting (Old Style)
This method is older and similar to C-style formatting.
"%s is %d years old" % ("Alice", 25)
Output:
Alice is 25 years old
Format Specifiers:
Format | Meaning |
---|---|
%s |
String |
%d |
Integer |
%f |
Float |
Number Formatting
Decimal Places with f-strings:
pi = 3.14159
print(f"Value of pi: {pi:.2f}")
Output:
Value of pi: 3.14
Thousand Separators:
num = 1000000
print(f"{num:,}")
Output:
1,000,000
Alignment and Padding
You can align strings or numbers using f-strings or .format()
:
f-Strings:
print(f"{'left':<10} | {'center':^10} | {'right':>10}")
Output:
left | center | right
Format method:
print("{:<10} {:^10} {:>10}".format("left", "center", "right"))
Formatting with Dictionaries and Lists
From a dictionary:
person = {"name": "Alice", "age": 25}
print("{name} is {age} years old".format(**person))
From a list:
values = ["Alice", 25]
print("{} is {} years old".format(*values))
Complete Example: Generating a Report
def generate_report(name, score, total):
percentage = (score / total) * 100
print(f"Student: {name}")
print(f"Score: {score}/{total}")
print(f"Percentage: {percentage:.2f}%")
print(f"{'Status:':<10} {'Passed' if percentage >= 50 else 'Failed'}")
generate_report("Alice", 78, 100)
Output:
Student: Alice
Score: 78/100
Percentage: 78.00%
Status: Passed
Tips
✅ Prefer f-strings for readability and performance (Python 3.6+)
✅ Use .format()
if you need backward compatibility
✅ Always format numeric output for clarity (e.g., 2 decimal places)
✅ Use alignment and padding for table-like output
✅ For logging, consider using f-strings or template strings
⚠️ Common Pitfalls
Pitfall | Solution |
---|---|
Forgetting f in f-string |
f"{name}" , not "{name}" |
Mixing types improperly | Convert numbers to strings or use proper format specifiers |
Using old-style formatting with new Python features | Use f-strings in Python 3.6+ |
Overusing complex expressions in f-strings | Assign complex values to variables before formatting |
Summary
Python gives you multiple ways to format strings—each with its own strengths:
Method | Best For |
---|---|
f-Strings | Modern, readable, Python 3.6+ |
.format() |
Compatibility, flexibility |
% |
Legacy code or C programmers |
Start using f-strings
for most use cases, and you'll write cleaner and more intuitive string handling code.
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]) # 3
Let’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