Python Common Operations

• Initialize integer as positive or negative infinity: {python} i: int = float('-inf'|'inf')

Collections §

Sets §

• Set difference{python} set(list1) - set(list2)
  • $O(n)$
• Set lookup {python}i in {1, 2, 3}
  • ==Constant time $O(1)$ lookup==

List §

• List Sort {python} list2 = sorted(list1)
  • $O(n\log n)$
• Deduplication{python} list1 = list(set(list1))
  • $O(n)$
• Counter {python}Counter("mississippi")
  • returns {python}{'i': 4, 's': 4, 'p': 2, 'm': 1}
  • $O(n)$
• Accumulate{python} accumulate(list1)
  • $O(n)$

Dictionary §

• Default value for dictionary entries{python}dictionary = collections.defaultdict(list|int)
• Helps when you have a list of dicts, or accumulating a count in a dict.