RecursionError maximum recursion depth exceeded with an extended class from deque

Question

I implemented an extended class as following.

from collections import deque

class IntCollection(deque):
    def is_empty(self):
        return len(self) == 0

    def append(self, x):
        self.append(x)

And then:

a = IntCollection()
a.is_empty() --> True

Okay, that works. However, when I issued the below command, the RecursionError occurred:

a.append(1)

RecursionError                            Traceback (most recent call last)
<ipython-input-104-da0a5ad497c3> in <module>
----> 1 a.append(1)

<ipython-input-101-7eac8c051433> in append(self, x)
      6 
      7     def append(self, x):
----> 8         self.append(x)

... last 1 frames repeated, from the frame below ...

<ipython-input-101-7eac8c051433> in append(self, x)
      6 
      7     def append(self, x):
----> 8         self.append(x)

RecursionError: maximum recursion depth exceeded:

I didn't get the reason why I have this error. Anyone can explain? I use Python 3.9.4 by the way.

Answer 1

You're overriding the deque's append method. And when you call it it does nothing more than recursively call it again. Python has a maximum number of times a function can be called recursively, and after that it gives an error (RecursionError). Changing the name of the method to something else will work:

from collections import deque

class IntCollection(deque):
    def is_empty(self):
        return len(self) == 0

    def update(self, x):  # <-- change this name
        self.append(x)
        
a = IntCollection()
# now this work fine
a.update(1)