What is the format of a git tag object and how to calculate its SHA?

Question

I am familiar with how Git creates SHA1 hashes for files (blobs), but not how they are created for tag objects. I assume they are, if I create an annotated tag, but what is

Answer 1

The content of a tag object is as follows:

object 
type commit
tag 
tagger 

Based on that text the SHA1 value is calculated.

how might I replicate it outside of Git (e.g., in Perl or Python)?

Take a look at libgit2 and its various bindings.