formatting strings in python

There are a number of different ways to write / format strings in Python.

1. %-formatting
2. Str.format()
3. f-strings
4. Template Strings

This GeeksforGeeks article is a helpful resource on the differences.

Coming from Javascript, I thought Template strings would be what I’m most comfortable with, but it’s actually f-strings.

Printing “Hello, World!” in four ways:

str1 = "Hello"
str2 = "World"

# %-formatting
print("% s, % s!"%(str1, str2))

# Str.format()
print("{0}, {1}!".format(str1, str2))
print("{s1}, {s2}!".format(s1 = str1, s2 = str2))

# f-strings
print(f"{str1}, {str2}!")

# Template Strings
from string import Template
template = Template('$s1, $s2!')
print(template.substitute(s1 = str1, s2 = str2))

template2 = Template('${s1}, ${s2}!') # braces also work
print(template2.substitute(s1 = str1, s2 = str2))

Notes:

1. I looked at the example for the %-formatting a number of times before I actually noticed the syntax - % s represents the place for a string. The arguments are positional and can be referenced at the closing of the quotes.
2. Str.format() can use positional or named arguments. If named, their scope is limited to the arguments of .format, so they need to be assigned there, i.e. print("{str1}".format()) will return a KeyError for an undefined str1.