[python] Why can't I use a list as a dict key in python?

According to the Python 2.7.2 documentation:

An object is hashable if it has a hash value which never changes during its lifetime (it needs a hash() method), and can be compared to other objects (it needs an eq() or cmp() method). Hashable objects which compare equal must have the same hash value.

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.

All of Python’s immutable built-in objects are hashable, while no mutable containers (such as lists or dictionaries) are. Objects which are instances of user-defined classes are hashable by default; they all compare unequal, and their hash value is their id().

A tuple is immutable in the sense that you cannot add, remove or replace its elements, but the elements themselves may be mutable. List's hash value depends on the hash values of its elements, and so it changes when you change the elements.

Using id's for list hashes would imply that all lists compare differently, which would be surprising and inconvenient.

Examples related to python

programming a servo thru a barometer Is there a way to view two blocks of code from the same file simultaneously in Sublime Text? python variable NameError Why my regexp for hyphenated words doesn't work? Comparing a variable with a string python not working when redirecting from bash script is it possible to add colors to python output? Get Public URL for File - Google Cloud Storage - App Engine (Python) Real time face detection OpenCV, Python xlrd.biffh.XLRDError: Excel xlsx file; not supported Could not load dynamic library 'cudart64_101.dll' on tensorflow CPU-only installation

Examples related to list

Convert List to Pandas Dataframe Column Python find elements in one list that are not in the other Sorting a list with stream.sorted() in Java Python Loop: List Index Out of Range How to combine two lists in R How do I multiply each element in a list by a number? Save a list to a .txt file The most efficient way to remove first N elements in a list? TypeError: list indices must be integers or slices, not str Parse JSON String into List<string>

Examples related to dictionary

JS map return object python JSON object must be str, bytes or bytearray, not 'dict Python update a key in dict if it doesn't exist How to update the value of a key in a dictionary in Python? How to map an array of objects in React C# Dictionary get item by index Are dictionaries ordered in Python 3.6+? Split / Explode a column of dictionaries into separate columns with pandas Writing a dictionary to a text file? enumerate() for dictionary in python

Examples related to tuples

Append a tuple to a list - what's the difference between two ways? How can I access each element of a pair in a pair list? pop/remove items out of a python tuple Python convert tuple to string django: TypeError: 'tuple' object is not callable Why is there no tuple comprehension in Python? Python add item to the tuple Converting string to tuple without splitting characters Convert tuple to list and back How to form tuple column from two columns in Pandas

Examples related to hashable

Why can't I use a list as a dict key in python?