5.18 Hands-on Exercises

Practice Programs

• Write a function that takes a list of mixed types and returns counts of how many are int, str, and float.
• Given a list with duplicate IP addresses, return only the unique ones using a set.
• Write a function demonstrating the mutable-default-argument bug, then fix it.
• Parse a small JSON config string and print the type of each top-level value.
• Write a script that shows id() staying the same after list.append() but changing after tuple concatenation.

Mini Projects

• Config loader — read a dict of settings, validate each value’s type with isinstance(), and raise a clear error for any mismatch.
• IP-address deduplicator — read a list of IPs from a (simulated) log file and report unique vs total counts using a set.
• Type profiler — given any object, print its type, id, and whether it’s mutable or immutable (based on a lookup table of known types).

Quick Interview Answer

“These exercises reinforce the chapter’s core ideas hands-on: counting types in a mixed list exercises type()/isinstance(), deduplicating IPs exercises set, the mutable-default-argument fix exercises function default semantics, and the type profiler exercises identity (id()) plus the mutable/immutable distinction from 5.9 Mutable vs Immutable Types together.”

Common Mistakes

• Skipping the mutable-default exercise as “just theory” — it’s one of the most common real bugs in production Python code.
• Building the type profiler with a hardcoded if/elif chain per type instead of a lookup table, making it harder to extend.