Core Python Programming (2nd Edition)

8.9. pass Statement
One Python statement not found in C is the pass statement. Because Python does not use curly braces
to delimit blocks of code, there are places where code is syntactically required. We do not have the
equivalent empty braces or single semicolon the way C does to indicate "do nothing." If you use a
Python statement that expects a sub-block of code or suite, and one is not present, you will get a syntax
error condition. For this reason, we have pass, a statement that does absolutely nothingit is a true NOP,
to steal the "No OPeration" assembly code jargon. Style- and development-wise, pass is also useful in
places where your code will eventually go, but has not been written yet (in stubs, for example):
def foo_func():
pass
or
if user_choice == 'do_calc':
pass
else:
pass
This code structure is helpful during the development or debugging stages because you want the
structure to be there while the code is being created, but you do not want it to interfere with the other
parts of the code that have been completed already. In places where you want nothing to execute, pass
is a good tool to have in the box.
Another popular place is with exception handling, which we will take a look at in Chapter 10; this is
where you can track an error if it occurs, but take no action if it is not fatal (you just want to keep a
record of the event or perform an operation under the covers if an error occurs).