Why do we need tuples in Python (or any immutable data type)?

by

  1. immutable objects can allow substantial optimization; this is presumably why strings are also immutable in Java, developed quite separately but about the same time as Python, and just about everything is immutable in truly-functional languages.

  2. in Python in particular, only immutables can be hashable (and, therefore, members of sets, or keys in dictionaries). Again, this afford optimization, but far more than just “substantial” (designing decent hash tables storing completely mutable objects is a nightmare — either you take copies of everything as soon as you hash it, or the nightmare of checking whether the object’s hash has changed since you last took a reference to it rears its ugly head).

Example of optimization issue:

$ python -mtimeit '["fee", "fie", "fo", "fum"]'
1000000 loops, best of 3: 0.432 usec per loop
$ python -mtimeit '("fee", "fie", "fo", "fum")'
10000000 loops, best of 3: 0.0563 usec per loop

More Related Contents:

  1. how to unpack a tuple in this form (‘abc’, [20, 20])? [closed]
  2. Sort a list of tuples by 2nd item (integer value) [duplicate]
  3. Why can’t I use a list as a dict key in python?
  4. Why does adding a trailing comma after a variable name make it a tuple?
  5. Expanding tuples into arguments
  6. How are tuples unpacked in for loops?
  7. Why can tuples contain mutable items?
  8. How to convert comma-delimited string to list in Python?
  9. Convert tuple to list and back
  10. Unpacking a list / tuple of pairs into two lists / tuples
  11. Convert list to tuple in Python
  12. How to form tuple column from two columns in Pandas
  13. Explicitly select items from a list or tuple
  14. How to convert a list to a list of tuples?
  15. Transform “list of tuples” into a flat list or a matrix
  16. Convert RGB color to English color name, like ‘green’ with Python
  17. How to compare a list of lists/sets in python?
  18. Tuple or list when using ‘in’ in an ‘if’ clause?
  19. Sorting a tuple that contains tuples
  20. How to convert nested list of lists into a list of tuples in python 3.3?
  21. Convert a columns of string to list in pandas
  22. What is the pythonic way to unpack tuples as function arguments? [duplicate]
  23. How to create a “singleton” tuple with only one element
  24. Why can’t I use a list as a dict key in python? Exactly what can and cannot be used, and why?
  25. Does Python have an immutable list?
  26. How to check if a tuple contains an element in Python?
  27. Swap values in a tuple/list inside a list in python?
  28. python – get list of tuples first index?
  29. Generate all subsets of size k (containing k elements) in Python
  30. In what case would I use a tuple as a dictionary key? [closed]

Leave a Comment