0-1 Sequences (failed time limit)

sequences.py

@@ -0,0 +1,47 @@
+import enum
+
+
+def count_inversions(seq: str)-> int:
+    inversions = 0
+    count = 0
+    for i, c in enumerate(seq):
+        if c == '0':
+            inversions += i - count
+            count += 1
+    return inversions
+
+class sequence_generator:
+    def __init__(self, seq: str):
+        self._seq = seq
+        self.qpos = []
+        for i, c in enumerate(seq):
+            if c == '?':
+                self.qpos.append(i)
+    
+    def __iter__(self):
+        self.max = pow(2, len(self.qpos))
+        self.current = 0
+        return self
+    
+    def __next__(self):
+        if self.current < self.max:
+            new_seq = self._seq
+            bstr = "{0:b}".format(self.current)
+            bstr = "".join(("0" * (len("{0:b}".format(self.max)) - len(bstr) - 1), bstr))
+            for i, c in enumerate(bstr):
+                new_seq = f"{new_seq[:self.qpos[i]]}{c}{new_seq[self.qpos[i]+1:]}"
+            self.current += 1
+            return new_seq
+        raise StopIteration
+
+
+seq = input()
+if "?" not in seq:
+    sum = count_inversions(seq)
+else:
+    s = sequence_generator(seq)
+    sum = 0
+    for x in s:
+        sum += count_inversions(x)
+
+print(sum % 1000000007)