Sorting Structures

Sorting is a core operation in data structures.

Python provides:

• sorted() (returns new list)
• list.sort() (sorts in place)

Sort numbers

nums = [5, 2, 8, 1]
print(sorted(nums))

Sort strings

words = ["banana", "apple", "kiwi"]
words.sort()
print(words)

Sort by custom key (very important)

Sort by length:

words = ["apple", "hi", "banana", "kiwi"]
words.sort(key=len)
print(words)

Sort dicts in a list

students = [
  {"name": "Tom", "grade": 85},
  {"name": "Sarah", "grade": 92},
  {"name": "Mike", "grade": 78},
]
students.sort(key=lambda s: s["grade"], reverse=True)
print(students)

Multiple keys

Sort by grade then name:

data = [("Tom", 25), ("Sarah", 25), ("Mike", 30)]
data.sort(key=lambda x: (x[1], x[0]))
print(data)

Graph: sorting pipeline

flowchart LR
  A[Unsorted list] --> B[key function]
  B --> C[Order by key]
  C --> D[Sorted list]

Remember

• sorted() makes a new list, sort() changes existing list
• key= is the power tool
• Python sorting is stable (keeps relative order when keys tie)