Use dictionary word anywhere in the mask

[undeath]

note about your python script: specify the command as list of strings and you don't have to worry about any kind of escaping.

but anyway, just generate a rule file with pattern ^?a and one with $?a and then run commands like
hashcat -a0 hash.txt wordlist.txt -r append-char.rule -r append-char.rule -r prepend-char.rule