List, tuple and dict

• list and tuple are popular types in Python to treat a set of variables.

list

• A set of variables can be stored in list.

  float_list  = [1, 2, 3]
  string_list = ["A", "B", "Three"]
  

• The elements in the list can be accessed with index.

  float_list[0]  # => 1
  float_list[0] = 0  # replacing the element
  

• Note that, in Python, the index starts with zero (not one); list[0] is the first element and list[1] is the second element.
• You can obtain the length of the list with len function.

  a = [1, 2, 3]
  len(a)
  

• You can combine lists as

  [0, 1, 2] + [3, 4]  # => [0, 1, 2, 3, 4, 5]
  

• Multiplication is also possible

  a = [0] * 10  # => [0, 0, 0, ..., 0]
  

• You can append an element with append

  a = [0, 1]
  a.append(2)
  a  # => [0, 1, 2]
  

• remove

  a = [0, 1]
  a.remove(0)
  print(a)
  

• extend

  a = [0, 1]
  b = [2, 3]
  c = a + b    # need to store in the different list
  a.extend(b)  # a is extended
  print(a)
  print(c)
  

Index slicing

• You can access the index of the list as follows: x[start=0 : stop=size : step=1]
• This is called slicing, and in the script you do like

  a = [1]*10
  print(a[:])    # all elements
  print(a[0:9])  # from 0 to 8 (not 9!)
  print(a[:5])   # from 0 to 4
  print(a[4:])   # from 5 to the last(10)
  

Tuple

• Tuple is similar to a list, but different way of treating a data set.

  a = (0, 1, 2)
  

• The biggest difference is that you cannot replace the element in a tuple afterward.

  a = (0, 1, 2)
  a[0] = 10  # => error
  

dict

• dict is a special type that allows making key and value pair.
• key and value is separated with colon (:).

  d = {"Apple": 100}
  

• Here "Apple" is key and 100 is value. You can access the value by specifying the key.

  d = {"Apple": 100, "Orange": 120}
  print(d["Orange"])
  

• You can add the key-value pair to the dict by | or update function.

  a = {"Apple": 100}
  b = {"Banana": 200}
  c = a | b
  print(c)
  

  or

  d = {"Apple": 100}
  d.update({"Banana": 200})
  print(d)
  

• To loop over dict,

  d = {"Apple": 120, "Orange": 110, "Banana": 200}
  for i, j in d.items():
      print(i, "is", j, "Yen.")
  

• Setting initial values to dict from key can be done by .fromkeys().

  keys = {"a", "b", "c"}
  {}.fromkeys(keys, 0)  # --> {"a": 0, "b": 0, "c": 0}
  

Exercise

• Create a dictionary representing a person's information (name, age, city) and access specific elements. answer