Factor out utility methods

bytetrie/bytetrie.py

@@ -1,6 +1,8 @@
 from __future__ import annotations
 from typing import Sequence, MutableSequence, ByteString, Any, Optional
 from abc import ABC, abstractmethod
+from .util import (has_common_prefix, common_prefix, is_prefix_of, find_first,
+                   cut_off_prefix)
 
 import logging
 log = logging.getLogger(__name__)
@@ -97,36 +99,6 @@ class ByteTrie:
     def to_dot(self) -> str:
         return "graph {\n\n"+self.root.to_dot()+"\n}"
 
-def has_common_prefix(label: ByteString, other_label: ByteString) -> bool:
-    """ Whether label and other_label have a prefix in common. """
-    assert label and other_label
-    return True if label[0] == other_label[0] else False
-
-def common_prefix(label: ByteString, other_label: ByteString) -> ByteString:
-    """ Get the common prefix of label and other_label. """
-    buffer = bytearray()
-    for (a,b) in zip(label, other_label):
-        if a == b: buffer.append(a)
-        else: break
-    return buffer
-
-def is_prefix_of(prefix: ByteString, label: ByteString) -> bool:
-    """ Whether label starts with prefix """
-    if len(prefix) > len(label):
-        return False
-    for (a,b) in zip(prefix, label):
-        if a != b: return False
-    return True
-
-def find_first(predicate, iterable):
-    """ Return the first element in iterable that satisfies predicate or None """
-    try: return next(filter(predicate, iterable))
-    except StopIteration: return None
-
-def cut_off_prefix(prefix: ByteString, label: ByteString) -> ByteString:
-    """ Cut prefix from start of label. Return rest of label. """
-    assert is_prefix_of(prefix, label)
-    return bytes(label[len(prefix):])
 
 class Node(ABC):
     def __init__(self, children: MutableSequence[Child]):

bytetrie/util.py

@@ -0,0 +1,30 @@
+def has_common_prefix(label: ByteString, other_label: ByteString) -> bool:
+    """ Whether label and other_label have a prefix in common. """
+    assert label and other_label
+    return True if label[0] == other_label[0] else False
+
+def common_prefix(label: ByteString, other_label: ByteString) -> ByteString:
+    """ Get the common prefix of label and other_label. """
+    buffer = bytearray()
+    for (a,b) in zip(label, other_label):
+        if a == b: buffer.append(a)
+        else: break
+    return buffer
+
+def is_prefix_of(prefix: ByteString, label: ByteString) -> bool:
+    """ Whether label starts with prefix """
+    if len(prefix) > len(label):
+        return False
+    for (a,b) in zip(prefix, label):
+        if a != b: return False
+    return True
+
+def find_first(predicate, iterable):
+    """ Return the first element in iterable that satisfies predicate or None """
+    try: return next(filter(predicate, iterable))
+    except StopIteration: return None
+
+def cut_off_prefix(prefix: ByteString, label: ByteString) -> ByteString:
+    """ Cut prefix from start of label. Return rest of label. """
+    assert is_prefix_of(prefix, label)
+    return bytes(label[len(prefix):])