Different meanings of brackets in Python

[]: Lists and indexing/lookup/slicing

• Lists: [], [1, 2, 3], [i**2 for i in range(5)]
• Indexing: 'abc'[0] → 'a'
• Lookup: {0: 10}[0] → 10
• Slicing: 'abc'[:2] → 'ab'

(): Tuples, order of operations, generator expressions, function calls and other syntax.

• Tuples: (), (1, 2, 3)
  • Although tuples can be created without parentheses: t = 1, 2 → (1, 2)
• Order of operations: (n-1)**2
• Generator expression: (i**2 for i in range(5))
• Function or method calls: print(), int(), range(5), '1 2'.split(' ')
  • with a generator expression: sum(i**2 for i in range(5))

{}: Dictionaries and sets

• Dicts: {}, {0: 10}, {i: i**2 for i in range(5)}
• Sets: {0}, {i**2 for i in range(5)}