Dictionaries Basics

Creating Dictionaries

  1. # create dict
  2. person = {"name": "Alice", "age": 25}
  3. empty = {}
  4. scores = {"math": 90, "english": 85}

Accessing Values

  1. # access by key
  2. person = {"name": "Alice", "age": 25}
  3. person["name"]
  4. #ans: "Alice"
  5. person["age"]
  6. #ans: 25

Get Method

  1. # get with default
  2. person = {"name": "Alice"}
  3. person.get("age")
  4. #ans: None
  5. person.get("age", 0)
  6. #ans: 0

Adding/Updating

  1. # add new key
  2. person = {"name": "Alice"}
  3. person["age"] = 25
  4. #ans: {"name": "Alice", "age": 25}
  5. #ans: update existing
  6. person["age"] = 26
  7. #ans: {"name": "Alice", "age": 26}

Deleting Items

  1. # delete key
  2. person = {"name": "Alice", "age": 25}
  3. del person["age"]
  4. #ans: {"name": "Alice"}

Keys, Values, Items

  1. # get keys, values, items
  2. person = {"name": "Alice", "age": 25}
  3. person.keys()
  4. #ans: dict_keys(['name', 'age'])
  5. person.values()
  6. #ans: dict_values(['Alice', 25])
  7. person.items()
  8. #ans: dict_items([('name', 'Alice'), ('age', 25)])

Exercises - Part 1

  1. # what is the value?
  2. d = {"a": 1, "b": 2}
  3. d["a"]
  4. #ans: 1

Exercises - Part 2

  1. # key not found?
  2. d = {"a": 1}
  3. d["b"]
  4. #ans: KeyError

Exercises - Part 3

  1. # get vs brackets?
  2. d = {"a": 1}
  3. d.get("b")
  4. #ans: None
  5. d["b"]
  6. #ans: KeyError

Exercises - Part 4

  1. # adding new key?
  2. d = {"a": 1}
  3. d["b"] = 2
  4. #ans: {"a": 1, "b": 2}

Exercises - Part 5

  1. # updating value?
  2. d = {"a": 1}
  3. d["a"] = 10
  4. #ans: {"a": 10}

Exercises - Part 6

  1. # membership test?
  2. d = {"a": 1, "b": 2}
  3. "a" in d
  4. #ans: True
  5. 1 in d
  6. #ans: False (checks keys, not values)

Exercises - Part 7

  1. # dict length?
  2. d = {"a": 1, "b": 2, "c": 3}
  3. len(d)
  4. #ans: 3

Exercises - Part 8

  1. # empty dict check?
  2. d = {}
  3. bool(d)
  4. #ans: False

Exercises - Part 9

  1. # nested dict?
  2. d = {"user": {"name": "Alice", "age": 25}}
  3. d["user"]["name"]
  4. #ans: "Alice"

Exercises - Part 10

  1. # dict from pairs?
  2. pairs = [("a", 1), ("b", 2)]
  3. d = dict(pairs)
  4. #ans: {"a": 1, "b": 2}

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