data-structures.md

Data Structures

• see https://docs.python.org/3/tutorial/datastructures.html
• no generics, collections contain just pointers to objects

Sequences

• last element - list[-1]

Sequences - Immutable

Strings

Tuples

• tuple = (1, "a", ("John", 33))
• similar to list but immutable
• operations are the same as for list
• syntax for single item tuple - (1,) or tuple(1)

Bytes

Sequences - Mutable

Lists

• list = [1, "a", ["nested", "list"]]
• convert from range - list(range(10))
• merge lists - merged = list1 + list2
• initializing lists - [0] * 5
• adding/removing elements

  list.insert(index, obj)
  list.remove(obj)
  list.append(obj) # push
  list.pop()
  list[:3] = [] # remove first 3 elements
  

• contains - in, not in
• sorting - list.sort()
• re-assign sublist
  • letters[2:5] = ['C', 'D', 'E']
  • letters[2:5] = ['C'] - this works as well

Byte arrays

Sets

• set = {1, "a"}
• empty set - set()
• can't contain mutable data structures (no lists, sets or dictionaries, tuples are OK)
• union - set1 | set2
• intersection - set1 & set2
• difference - set1 - set2
• set() vs {}
  • set() converts iterables into individual elements
    • set('foo') --> {'o', 'f'}
  • {'foo'} --> {'foo'}
• frozenset - immutable set, can be used as a hash

Frozen sets

• immutable, frozenset(..)

Mappings - Dictionaries

• my_dict = {"John": 33, "Jane": 28}, or my_dict = dict(John=33, Jane=28)
• unordered
• iteration - for name, age in my_dict.items():
• adding new entry - my_dict["Harry"] = 55
• contains a key - "foo" in my_dict
• removing a key - del my_dict["John"]
• list keys - list(my_dict)

Conversions

• list(..)
  • list(dict) - keys only
  • list(dict.items()) - list of tuples
• tuple(..)
• set(..)
• dict(..)