The string.Template (https://docs.python.org/3/library/string.html#template-strings) class allows to do $-style substitutions:
from string import Template
t = Template('Hello, $channel!')
t.substitute(dict(channel='@pythonetc'))
# 'Hello, @pythonetc!'
t.safe_substitute(dict())
# 'Hello, $channel!'
Initially, it was introduced (https://peps.python.org/pep-0292/) to simplify translations of strings. However, now PO-files (https://www.gnu.org/software/gettext/manual/html_node/PO-Files.html) natively support python-format (https://www.gnu.org/software/gettext/manual/html_node/python_002dformat.html) flag. It indicates for translators that the string has str.format-style substitutions. And on top of that, str.format is much more powerful and flexible.
Nowadays, the main purpose of Template is to confuse newbies with one more way to format a string (https://t.me/pythonetc/610). Jokes aside, there are a few more cases when it can come in handy:
+ Template.safe_substitute can be used when the template might have variables that aren't defined and should be ignored.
+ The substitution format is similar to the string substitution in bash (and other shells), which is useful in some cases. For instance, if you want to write your own dotenv (https://github.com/motdotla/dotenv).
