I have been trying to deconstruct a string in the following way:
str = 'Hello world I am Bob'
sub_str1 = 'Hello world'
sub_str2 = 'world I'
answer = ' I am Bob'
answer = 'Hello I am Bob'
replace parts of a string with some other string.
"Substracting" would be replacing a substring with an empty string:
>>> 'Hello world I am Bob'.replace('Hello world', '') ' I am Bob'