I have a Pair class (it has a key and a value) and I'm trying to make a program which creates a bunch of Pair objects, adds them to a list, and performs stable quicksort on them. However, I can't seem to figure how to make the objects comparable so that the program automatically compares the keys of two objects when they have the same value. It's so easy to do this in Java but I just don't get how I'm supposed to do the equivalent in Python.
Thank you in advance!
class Pair(Generic[K,V]):
def __init__(self, key: K, val: V):
self.key = key
self.value = val
How about the following (Pair sortable by key but you can easily define any other way to sort them):
class Pair:
def __init__(self, key, val):
self.key = key
self.value = val
def __eq__(self, other: "Pair"):
return self.key == other.key
def __lt__(self, other: "Pair"):
return self.key < other.key
def __le__(self, other: "Pair"):
return self.key <= other.key
def __gt__(self, other: "Pair"):
return self.key > other.key
def __ge__(self, other: "Pair"):
return self.key >= other.key
def __str__(self):
return f"{self.key}={self.value}"
def __repr__(self):
return f"{self.key}={self.value} ({id(self)})"
test = [
Pair("a2", "1"), Pair("a1", "2"), Pair("b1", "3"),Pair("br", "4")
]
print(sorted(test))
Output:
$ python3 ~/tmp/test.py
[a1=2 (4352627216), a2=1 (4352622288), b1=3 (4352627344), br=4 (4352627408)]
To sort by value and then by key if the values are equal you would dp something like:
def __lt__(self, other: "Pair"):
if self.value != other.value:
return self.value < other.value
return self.key < other.key
example input/output with the above lt:
# Input
test = [
Pair("a2", "1"), Pair("a1", "2"), Pair("b1", "1"),Pair("br", "4")
]
# Output
[a2=1 (4466773648), b1=1 (4466778768), a1=2 (4466778640), br=4 (4466778832)]
Additionally, if you plan to use the pairs as dictionary keys or in sets you can implement __hash__. For more operators see here