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Day 5 — Python dictionaries, tuples and sets
A list remembers order. A dictionary remembers labels — and that is what most real data needs.
Dictionaries — key and value
Adding and changing
Asking for a key that is not there is an error
Use
.get() when a key might be missing — it returns None, or whatever default you give it, instead of stopping your program.Looping over a dictionary
keys, values, items
Tuples — a list that cannot change
That last line is unpacking, and it is everywhere in real Python.
Sets — unique values only
Which one do I use?
List when order matters and repeats are fine. Dictionary when each value has a label. Tuple when the group should not change. Set when you only care about unique values.
Try these yourself
- Build a dictionary for one customer with name, city and amount, then print just the city.
- Use .get() to ask for a key that does not exist.
- Loop over a dictionary of three sales reps and print each name and total.
- Count the unique values in [1,2,2,3,3,3].
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