Python F-Strings Tricks You Should Know

Unal Patel

May 8, 2023

Python F-Strings

Python F-strings are a handy tool for creating more readable and concise Python code. They allow you to embed variables and expressions inside string literals.

When processing f-strings, the parser pushes a new tokenizer mode on top of the regular Python tokenizer mode stack. This mode usually tokenizes the f-string expression part until a:,! or = character is encountered.

Embedded f-strings

F-strings are an improved way of formatting strings in Python. They allow variables, functions, and expressions to be embedded within the string. They were introduced in Python 3.6 and had many handy features that save you time when formatting numbers, dates and other strings.

When creating an f-string, the literal portion is defined in curly braces and the expression part is written inside single or double quotes. If you try to use the backslash escape character in the expression portion of an f-string, it will not be valid and cause a syntax error.

When you run the f-string, Python will evaluate the expressions inside of it and replace them with their values. For example, if you have an f-string like ‘f’+’numbers[0]1+2’, Python will evaluate that expression at runtime and return 3. This is much faster than using the str. format() method for the same purpose, especially when working with large numbers and dates that need to be formatted quickly and often.

Variables inside f-strings

Python f strings can contain any type of expression, such as the contents of a variable, the result of a mathematical calculation or another Python value. When such an expression is included in the f string, it will be represented as a string with a predefined __str__ method that coerces the included object into a string so that it can be printed out.

Like the format() method of str, f strings also support a replacement field with positional or keyword arguments. And just like the str() method, various formats can be achieved using a format specification string (such as fax).

F-strings are a faster, more readable and less error-prone way to format strings than traditional string formatting. They’re packed with valuable features that can be very helpful in day-to-day programming tasks. So make sure to use them when necessary. Happy coding!

Using f-strings to format dates

Although f-strings are a relatively new feature introduced in Python 3.6, they’re already packed with many handy features. These include formatting values, embedding expressions inside f-strings, and using conditional statements within f-strings.

Another valuable feature of f-strings is the ability to use string interpolation with them. This allows you to get a variable’s value alongside its name. This is very useful when debugging, as it makes it easier to see what the variable is doing.

It would be best to include the variable name in curly braces to do this. This will cause the f-string to be evaluated at runtime and then replace the variable’s name with its value. For example, if the variable is named “language”, the f-string will output “This book is about language”. If the variable is called “school”, the f-string will output “I’m learning Python at freeCodeCamp”. In addition, you can also format numbers and dates with f-strings.

Using f-strings to format numbers

F-strings are a powerful feature introduced in Python 3.6 that allows you to embed expressions into strings and have them evaluated at runtime. You can use f-strings to format numbers, evaluate expressions, and even incorporate lambda functions and methods into ropes.

You can use the ‘x’ format specification string to format a number in hexadecimal form. This is useful if you’re working with large numbers that must be displayed in a small space.

Another helpful option is the ‘n’ format string. This will format a number with a trailing space to make it more readable.

You can also use f-strings to format numbers as percentages. For example, if you use the ‘f%n’ format specification string, Python will automatically multiply the number by 100 and add decimal points for precision. It will also format the number in scientific notation if it’s a float. This is an efficient way to handle number formatting.