Better Flow Control with Python — First published in fullweb.io issue #32

python-better-flow-control.md

Better Flow Control with Python

I recently interviewed 4 developers for a Python programming position They all knew how to use requests, call APIs and worked either with Django or Flask, but I saw all of them ignoring most of Python’s specific control flow.

Here are two of them, try/except/else/finally and for/else:

try: 
    # What you want to do, which might
    # very well raise an exception
except IndexError as ex: 
    # What do to when IndexError is raised
except MyModule.itsException as ex: 
    # What do to when MyModule raised an exception
except Exception as ex: 
    # What do to when any other Exception is raised
else:
    # Something specific to Python
    # This is executed when try did NOT raised any exception
finally: 
    # Exception or not, always excecute this block,
    # even if a return statement is above

for item in mylist:
    # Processing each item here
else:
    # This is executed when the loop terminates through
    # exhaustion of the list (with for) or when the
    # condition becomes false (with while), but not when
    # the loop is terminated by a break statement.

A Fullweb reader contacted me to highlight this:

Item 12 of Brett Slatkin’s Effective Python:

"Avoid using else blocks after loops because their behaviour isn’t intuitive and can be confusing."