NotesPythonData Structures

Dictionaries

Key–value pairs — the structure behind most real-world data in Python.

A dictionary stores key–value pairs. Keys must be unique and hashable (strings, numbers, and tuples of immutables all work); values can be anything.

channel = {
    "name": "CodeWithMunnaX",
    "subscribers": 250_000,
    "verified": True,
}
print(channel["name"])          # 'CodeWithMunnaX'
channel["subscribers"] += 1000  # update a value
channel["platform"] = "YouTube" # add a new key

Avoiding KeyError

Indexing with [] raises KeyError if the key doesn't exist. .get() returns None (or a default you provide) instead.

print(channel.get("platform", "Unknown"))   # 'YouTube'
print(channel.get("country", "Unknown"))    # 'Unknown' -- no KeyError

Iterating a dictionary

for key in channel:                 # iterates keys by default
    print(key)

for key, value in channel.items():  # the one you'll use most
    print(key, "->", value)

for value in channel.values():
    print(value)

Since Python 3.7, dictionaries preserve insertion order — iterating gives you keys in the order they were added, not a random order.

Removing keys

channel.pop("verified")             # remove and return the value
del channel["platform"]             # remove without returning it

Merging dictionaries

defaults = {"theme": "dark", "autoplay": True}
overrides = {"autoplay": False}
settings = {**defaults, **overrides}   # later keys win on conflict
print(settings)   # {'theme': 'dark', 'autoplay': False}
Key points to remember
  • •dict[key] raises KeyError for a missing key; dict.get(key, default) doesn't.
  • •Dictionaries have preserved insertion order since Python 3.7 — iteration order matches how keys were added.
  • •for k, v in d.items(): is the standard way to loop over both keys and values together.
  • •{**a, **b} merges dictionaries; when both have the same key, the value from the later one wins.
  • •Keys must be hashable (immutable) — strings, numbers, and tuples of immutables work; lists and dicts don't.

Building and reading a channel profile

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TuplesSets