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#!/usr/bin/env python3
 
### 余再帰
class unfoldr:
    def __init__(self, f, seed):
        self.f = f
        self.seed = seed
    def __iter__(self):
        return self
    def __next__(self):
        match self.f(self.seed):
            case a, b:
                self.seed = b
                return a
            case None:
                raise StopIteration
    def __reversed__(self):
        return reversed(self)
 
def primes():
    yield 2
    for i in filter(is_prime, unfoldr(lambda x: (x, x + 1), 3)):
        yield i
 
def is_prime(n):
    for i in primes():
        if i ** 2 > n:
            return True
        elif n % i == 0:
            return False
        else:
            continue
 

Traceback (most recent call last):
  File "/usr/lib/python3.9/py_compile.py", line 144, in compile
    code = loader.source_to_code(source_bytes, dfile or file,
  File "<frozen importlib._bootstrap_external>", line 918, in source_to_code
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "./prog.py", line 11
    match self.f(self.seed):
          ^
SyntaxError: invalid syntax

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.9/py_compile.py", line 150, in compile
    raise py_exc
py_compile.PyCompileError:   File "./prog.py", line 11
    match self.f(self.seed):
          ^
SyntaxError: invalid syntax

Standard output is empty