Wrap up low level placeholder handling into PlaceholderConfig helper class. (#96)

Author: ianjosephwilson

tdom/placeholders.py

@@ -1,63 +1,72 @@
+from dataclasses import dataclass, field
 import random
 import re
 import string
 
 from .template_utils import TemplateRef
 
 
-_PLACEHOLDER_PREFIX = f"t🐍{''.join(random.choices(string.ascii_lowercase, k=2))}-"
-_PLACEHOLDER_SUFFIX = f"-{''.join(random.choices(string.ascii_lowercase, k=2))}🐍t"
-_PLACEHOLDER_PATTERN = re.compile(
-    re.escape(_PLACEHOLDER_PREFIX) + r"(\d+)" + re.escape(_PLACEHOLDER_SUFFIX)
-)
+def make_placeholder_config() -> PlaceholderConfig:
+    prefix = f"t🐍{''.join(random.choices(string.ascii_lowercase, k=2))}-"
+    suffix = f"-{''.join(random.choices(string.ascii_lowercase, k=2))}🐍t"
+    return PlaceholderConfig(
+        prefix=prefix,
+        suffix=suffix,
+        pattern=re.compile(re.escape(prefix) + r"(\d+)" + re.escape(suffix)),
+    )
 
 
-def make_placeholder(i: int) -> str:
-    """Generate a placeholder for the i-th interpolation."""
-    return f"{_PLACEHOLDER_PREFIX}{i}{_PLACEHOLDER_SUFFIX}"
+@dataclass(frozen=True)
+class PlaceholderConfig:
+    """String operations for working with a placeholder pattern."""
 
+    prefix: str
+    suffix: str
+    pattern: re.Pattern
 
-def match_placeholders(s: str) -> list[re.Match[str]]:
-    """Find all placeholders in a string."""
-    return list(_PLACEHOLDER_PATTERN.finditer(s))
+    def make_placeholder(self, i: int) -> str:
+        """Generate a placeholder for the i-th interpolation."""
+        return f"{self.prefix}{i}{self.suffix}"
 
+    def match_placeholders(self, s: str) -> list[re.Match[str]]:
+        """Find all placeholders in a string."""
+        return list(self.pattern.finditer(s))
 
-def find_placeholders(s: str) -> TemplateRef:
-    """
-    Find all placeholders in a string and return a TemplateRef.
+    def find_placeholders(self, s: str) -> TemplateRef:
+        """
+        Find all placeholders in a string and return a TemplateRef.
 
-    If no placeholders are found, returns a static TemplateRef.
-    """
-    matches = match_placeholders(s)
-    if not matches:
-        return TemplateRef.literal(s)
+        If no placeholders are found, returns a static TemplateRef.
+        """
+        matches = self.match_placeholders(s)
+        if not matches:
+            return TemplateRef.literal(s)
 
-    strings: list[str] = []
-    i_indexes: list[int] = []
-    last_index = 0
-    for match in matches:
-        start, end = match.span()
-        strings.append(s[last_index:start])
-        i_indexes.append(int(match[1]))
-        last_index = end
-    strings.append(s[last_index:])
+        strings: list[str] = []
+        i_indexes: list[int] = []
+        last_index = 0
+        for match in matches:
+            start, end = match.span()
+            strings.append(s[last_index:start])
+            i_indexes.append(int(match[1]))
+            last_index = end
+        strings.append(s[last_index:])
 
-    return TemplateRef(tuple(strings), tuple(i_indexes))
+        return TemplateRef(tuple(strings), tuple(i_indexes))
 
 
+@dataclass
 class PlaceholderState:
-    known: set[int]
+    known: set[int] = field(default_factory=set)
+    config: PlaceholderConfig = field(default_factory=make_placeholder_config)
     """Collection of currently 'known and active' placeholder indexes."""
 
-    def __init__(self):
-        self.known = set()
-
     @property
     def is_empty(self) -> bool:
         return len(self.known) == 0
 
     def add_placeholder(self, index: int) -> str:
-        placeholder = make_placeholder(index)
+        placeholder = self.config.make_placeholder(index)
         self.known.add(index)
         return placeholder
 
@@ -69,7 +78,7 @@ def remove_placeholders(self, text: str) -> TemplateRef:
 
         If no placeholders are found, returns a static PlaceholderRef.
         """
-        pt = find_placeholders(text)
+        pt = self.config.find_placeholders(text)
         for index in pt.i_indexes:
             if index not in self.known:
                 raise ValueError(f"Unknown placeholder index {index} found in text.")

tdom/placeholders_test.py

@@ -1,52 +1,52 @@
 import pytest
 
 from .placeholders import (
-    _PLACEHOLDER_PREFIX,
-    _PLACEHOLDER_SUFFIX,
+    make_placeholder_config,
     PlaceholderState,
-    find_placeholders,
-    make_placeholder,
-    match_placeholders,
 )
 
 
 def test_make_placeholder() -> None:
-    assert make_placeholder(0) == f"{_PLACEHOLDER_PREFIX}0{_PLACEHOLDER_SUFFIX}"
-    assert make_placeholder(42) == f"{_PLACEHOLDER_PREFIX}42{_PLACEHOLDER_SUFFIX}"
+    config = make_placeholder_config()
+    assert config.make_placeholder(0) == f"{config.prefix}0{config.suffix}"
+    assert config.make_placeholder(42) == f"{config.prefix}42{config.suffix}"
 
 
 def test_match_placeholders() -> None:
-    s = f"Start {_PLACEHOLDER_PREFIX}0{_PLACEHOLDER_SUFFIX} middle {_PLACEHOLDER_PREFIX}1{_PLACEHOLDER_SUFFIX} end"
-    matches = match_placeholders(s)
+    config = make_placeholder_config()
+    s = f"Start {config.prefix}0{config.suffix} middle {config.prefix}1{config.suffix} end"
+    matches = config.match_placeholders(s)
     assert len(matches) == 2
-    assert matches[0].group(0) == f"{_PLACEHOLDER_PREFIX}0{_PLACEHOLDER_SUFFIX}"
+    assert matches[0].group(0) == f"{config.prefix}0{config.suffix}"
     assert matches[0][1] == "0"
-    assert matches[1].group(0) == f"{_PLACEHOLDER_PREFIX}1{_PLACEHOLDER_SUFFIX}"
+    assert matches[1].group(0) == f"{config.prefix}1{config.suffix}"
     assert matches[1][1] == "1"
 
 
 def test_find_placeholders() -> None:
-    s = f"Hello {_PLACEHOLDER_PREFIX}0{_PLACEHOLDER_SUFFIX}, today is {_PLACEHOLDER_PREFIX}1{_PLACEHOLDER_SUFFIX}."
-    pt = find_placeholders(s)
+    config = make_placeholder_config()
+    s = f"Hello {config.prefix}0{config.suffix}, today is {config.prefix}1{config.suffix}."
+    pt = config.find_placeholders(s)
     assert pt.strings == ("Hello ", ", today is ", ".")
     assert pt.i_indexes == (0, 1)
 
     literal_s = "No placeholders here."
-    literal_pt = find_placeholders(literal_s)
+    literal_pt = config.find_placeholders(literal_s)
     assert literal_pt.strings == (literal_s,)
     assert literal_pt.i_indexes == ()
 
 
 def test_placeholder_state() -> None:
-    state = PlaceholderState()
+    config = make_placeholder_config()
+    state = PlaceholderState(config=config)
     assert state.is_empty
 
     p0 = state.add_placeholder(0)
-    assert p0 == make_placeholder(0)
+    assert p0 == config.make_placeholder(0)
     assert not state.is_empty
 
     p1 = state.add_placeholder(1)
-    assert p1 == make_placeholder(1)
+    assert p1 == config.make_placeholder(1)
 
     text = f"Values: {p0}, {p1}"
     pt = state.remove_placeholders(text)
@@ -55,4 +55,4 @@ def test_placeholder_state() -> None:
     assert state.is_empty
 
     with pytest.raises(ValueError):
-        state.remove_placeholders(f"Unknown placeholder: {make_placeholder(2)}")
+        state.remove_placeholders(f"Unknown placeholder: {config.make_placeholder(2)}")

tdom/processor_test.py

@@ -7,7 +7,7 @@
 from markupsafe import Markup
 
 from .nodes import Comment, DocumentType, Element, Fragment, Node, Text
-from .placeholders import _PLACEHOLDER_PREFIX, _PLACEHOLDER_SUFFIX
+from .placeholders import make_placeholder_config
 from .processor import html
 
 # --------------------------------------------------------------------------
@@ -597,25 +597,25 @@ def test_interpolated_attribute_value_tricky_multiple_placeholders():
 
 
 def test_placeholder_collision_avoidance():
+    config = make_placeholder_config()
     # This test is to ensure that our placeholder detection avoids collisions
     # even with content that might look like a placeholder.
     tricky = "123"
     template = Template(
         '<div data-tricky="',
-        _PLACEHOLDER_PREFIX,
+        config.prefix,
         Interpolation(tricky, "tricky"),
-        _PLACEHOLDER_SUFFIX,
+        config.suffix,
         '"></div>',
     )
     node = html(template)
     assert node == Element(
         "div",
-        attrs={"data-tricky": _PLACEHOLDER_PREFIX + tricky + _PLACEHOLDER_SUFFIX},
+        attrs={"data-tricky": config.prefix + tricky + config.suffix},
         children=[],
     )
     assert (
-        str(node)
-        == f'<div data-tricky="{_PLACEHOLDER_PREFIX}{tricky}{_PLACEHOLDER_SUFFIX}"></div>'
+        str(node) == f'<div data-tricky="{config.prefix}{tricky}{config.suffix}"></div>'
     )