DRAFT Migrating from Python to Racket

Contents

• Idioms
• Performance pitfalls
• References

Idioms

• A Python "List" is an extensible vector of pointers.

Performance pitfalls

• Python Lists aren’t Racket Lists

  • use either Growable Vectors or RaList
    • Growable Vectors
    • RaList: Purely Functional Random-Access Lists

• Python append isn't Racket append.

  • Python's append adds a single element to the back of the List in amortized O(1) time.
  • Racket's append returns the concatenation of two or more Lists in O(n) time.
    • This makes it more similar to extend or + in Python.
  • Use the cons operator to add single elements to a Racket List (adding to the front of a Racket List is a O(1) operation).
  • Building a List from the front may result in elements being in reverse order, but it is faster and more idiomatic in Racket to build a List from the front and then correct the order by calling reverse. While this may seem counter-intuitive, reverse is relatively fast and won't change the time complexity of any O(n) or worse operations.

How to transliterate the loop/append example from python to Racket:

optionally also show the more native Racket idiom

References

• Choosing a data-structure
• Notes on data structures in Racket, with some performance considerations.