% operator

title: Python String Formatting description: If your are using Python 3.6+, string f-strings are the recommended way to format strings.

% operator

>>> name = 'Pete'
>>> 'Hello %s' % name

We can use the %d format specifier to convert an int value to a string:

>>> num = 5
>>> 'I have %d apples' % num

str.format

Python 3 introduced a new way to do string formatting that was later back-ported to Python 2.7. This makes the syntax for string formatting more regular.

>>> name = 'John'
>>> age = 20

>>> "Hello I'm {}, my age is {}".format(name, age)

>>> "Hello I'm {0}, my age is {1}".format(name, age)

Formatted String Literals or f-Strings

If your are using Python 3.6+, string f-Strings are the recommended way to format strings.

>>> name = 'Elizabeth'
>>> f'Hello {name}!'

It is even possible to do inline arithmetic with it:

>>> a = 5
>>> b = 10
>>> f'Five plus ten is {a + b} and not {2 * (a + b)}.'

Multiline f-Strings

>>> name = 'Robert'
>>> messages = 12
>>> (
... f'Hi, {name}. '
... f'You have {messages} unread messages'
... )

The = specifier

This will print the expression and its value:

>>> from datetime import datetime
>>> now = datetime.now().strftime("%b/%d/%Y - %H:%M:%S")
>>> f'date and time: {now=}'

Adding spaces or characters

>>> f"{name.upper() = :-^20}"
>>>
>>> f"{name.upper() = :^20}"
>>>
>>> f"{name.upper() = :20}"

Formatting Digits

Adding thousands separator

>>> a = 10000000
>>> f"{a:,}"

Rounding

>>> a = 3.1415926
>>> f"{a:.2f}"

Showing as Percentage

>>> a = 0.816562
>>> f"{a:.2%}"

Number formatting table

Template Strings

A simpler and less powerful mechanism, but it is recommended when handling strings generated by users. Due to their reduced complexity, template strings are a safer choice.

>>> from string import Template
>>> name = 'Elizabeth'
>>> t = Template('Hey $name!')
>>> t.substitute(name=name)