How does "__doc__ % globals()" work?

[Ethan Furman]

On 4/12/21 3:06 PM, Jaime wrote:
 > Hi all. Line 102 of https://github.com/python/peps/blob/master/pep2html.py says:
 >
 > print(__doc__ % globals(), file=out)
 >
 > I realise that globals() is a standard-library
 > built-in function that returns a dictionary representing the current
 > global symbol table, and that the result of this expression is the
 > value of the dictionary where the key is "__doc__"

This is not correct.

There are a couple ways to use %-interpolation:

     some_name = 'Jaime'

     # simple
     `hello, %s` % (some_name, )  # hello, Jaime

     # keyed
     `hello, %(a_name)s` % {'a_name': 'Ethan'}  # hello, Ethan

What you are seeing is the keyed version.  So, if the module had, for example:

     version = 1.3
     author = 'GvR'
     date = '2021-04-12'

and the doc string was

     __doc__ = "version %(version)s was initially created by %(author)s"

then

     __doc__ % globals()

would substitute the `author` and `version` keys into __doc__, and printing that would yield

     version 1.3 was initially created by GvR

Note that extra keys are ignored.

--
~Ethan~