相当于列表中另一个的python项目

Question

In python you can check if an item is in a list:

if item in lst:
   do_stuff()

However, how do I check if a LIKE item is in the list? The is operator checks for the actual object. The in operator does the same. Is there an equivalent operator of == for in ?

What I want would be something like

if item is_equal_to_another_in lst:
    do_stuff()

For example: I have a list of [item('a'), item('b'), item('c')] . If I create another item('a') it will be exactly like the one in our list, except it will fail the in statement because the one in our list is a different instance.

Answer 1

For lists, __contains__ just compares the object with the __eq__ ( == ) operator. If not defined, it fall through to is .

You probably have to define __eq__ for your specific definition of equality given your items .

---

In this example, I demonstrate how to compare two items based on the value of their attr attribute by performing a case insensitive comparison.

>>> class item:
...     def __init__(self,attr): self.attr = attr
...     def __eq__(self,o): return isinstance(o, item) and self.attr.lower() == o.attr.lower()
... 
>>> lst = [item("a"), item("b")]
>>> item("A") in lst
True
>>> item("a") in lst
True
>>> item("B") in lst
True
>>> item("C") in lst
False
>>> "A" in lst
False