What %s Means in Python – Secret Revealed!

%s is an argument specifier and is used for string formatting. It borrows its syntax from the C language. Simply put, it lets you add a value inside a string.

The value can be a string or any object that can get converted into a string, for example, number, list, etc.

 

All string values

Consider the following example.

 

name = input("Please insert your name: ")
song = input("What is your favorite song? " )
print("Hello %s! Would you like to listen to %s?" %(name, song))

 

In the above example, we take the name and the favorite song from the user and display a message using these values.

Moreover, we put %s as a placeholder at those places where you want values of variables.

A tuple containing values follows the format string, i.e., %(name, song). Remember to insert values in the same order you want to display them. In this case, the name will come first and then the song.

A sample output of the above example is given below.

 

Please insert your name: ashton
What is your favorite song? Perfect
Hello ashton! Would you like to listen to Perfect?

As you can see, this works as expected.

 

A single value

If we only have a single %s, then we can write a value without a tuple. Let’s see.

 

name = input("Please insert your name: ")
print("Hello %s!" % name)

 

Output

 

Please insert your name: Agar
Hello Agar!

 

Objects with a string representation

As already mentioned, a value can be any object that can get converted into a string. Let’s take an example.

 

name = "Smith"
score = [70, 80, 90, 100]
print("The score of %s in the last four matches: %s" % (name, score))

 

Output

 

The score of Smith in the last four matches: [70, 80, 90, 100]

 

As you can observe, we place a string and a list using the %s argument specifier. It converts the list to a string automatically.

Let’s take the same example and do it using the concatenation operator.

 

name = "Smith"
score = [70, 80, 90, 100]
print("The score of " + name + " in the last four matches " + str(score))

 

Output

The score of Smith in the last four matches [70, 80, 90, 100]

Here, unlike %s, we explicitly convert the list to a string and use + at every place we want to add a value.

 

TypeError

Moreover, the number of argument specifiers needs to be the same as the number of values in the tuple. If they are not, you will get an error. Let’s see.

 

name = input("Please insert your name: ")
song = input("What is your favorite song? " )
print("Hello %s! Would you like to listen to %s?" %(name))

 

Output

 

As you can see in the above output, the program throws a TypeError.

 

Mapping key

Instead of remembering the order in which you want to insert values, you can pass a mapping key to %s. Consider the following example to understand this concept.

 

name = "Ashton Agar"
age  = 20
print("My name is %(name)s and my age is %(age)s." %{"age":age, "name":name})

 

Output

 

My name is Ashton Agar and my age is 20.

 

In the above example, we pass a dictionary containing (key, value) pairs instead of a tuple. Moreover, the key is placed in between the % and s, which gets replaced by its value later. Therefore, we do not need to remember the order.

%s is an old method of formatting strings. Better techniques such as format() and f-strings have got introduced that are easier to use and provide more functionalities.