String formatting is a powerful feature in Python that allows you to embed expressions inside string literals. In this tutorial, we will cover the basics of string formatting in Python and explore how to use placeholders like %s and %d to insert values into strings.
Introduction to String Formatting
In Python, you can use the % operator to format strings. This operator takes a string on the left side and a tuple of values on the right side. The string contains placeholders that are replaced with the values from the tuple.
Placeholders in String Formatting
Placeholders are special characters in the string that are replaced with values. The most common placeholders are %s for strings and %d for decimal integers. Here is an example:
name = 'John'
age = 30
print('%s is %d years old' % (name, age))
This will output: John is 30 years old
How %s and %d Work
The %s placeholder calls the str() function on the argument, which converts it to a string. The %d placeholder, on the other hand, calls the int() function on the argument before calling str(), which means it will truncate any decimal numbers.
Here is an example that demonstrates the difference:
number = 42.5
print('%s %d' % (number, number))
This will output: 42.5 42
As you can see, the %d placeholder truncated the decimal part of the number.
Other Placeholders
There are many other placeholders available in Python, including:
%ffor floating-point numbers%gfor generic numbers (either fixed or exponential notation)%xfor hexadecimal integers%ofor octal integers
Here is an example that demonstrates how to use these placeholders:
number = 42.5
print('%s %d %f %g' % (number, number, number, number))
This will output: 42.5 42 42.500000 4.25e+01
Error Handling
If you try to use a placeholder with an argument that is not compatible, Python will raise a TypeError. For example:
name = 'John'
print('%d' % name)
This will raise: TypeError: %d format: a number is required, not str
Best Practices
When using string formatting in Python, it’s essential to choose the correct placeholder for your argument type. If you’re unsure what type an argument will be, use the %s placeholder, which will work with any type.
Also, consider using f-strings (available in Python 3.6 and later) or the str.format() method, which provide more flexibility and readability than the % operator.
Conclusion
String formatting is a powerful feature in Python that allows you to embed expressions inside string literals. By understanding how placeholders like %s and %d work, you can create robust and readable code that handles different types of arguments. Remember to choose the correct placeholder for your argument type and consider using f-strings or str.format() for more flexibility.