Initial implementation of regex sound changer

.gitignore

@@ -1 +1,2 @@
 .pytest*
+*__pycache__*

soundchanger.py

@@ -1,32 +0,0 @@
-import re
-
-
-class Change:
-    """
-    Instantiates a string representation of a sound change.
-    """
-
-    def __init__(self, change):
-        self.parse(change)
-
-    def __repr__(self):
-        return f"{self.b}>{self.a}/{self.f}_{self.t}"
-
-    def parse(self, change):
-        if '/' in change:
-            _change, _env = change.split('/')
-        else:
-            _change = change
-            _env = '_'
-        self.b, self.a = _change.split('>')
-        self.f, self.t = _env.split('_')
-        
-        if self.f.startswith("{") and self.f.endswith("}"):
-            self.f = self.f[1:-1].split(',')
-            self.f = f"[{''.join(self.f)}]"
-        if self.t.startswith("{") and self.t.endswith("}"):
-            self.t = self.t[1:-1].split(',')
-            self.t = f"[{''.join(self.t)}]"
-
-    def sub(self, string):
-        return re.sub(f"(?<={self.f}){self.b}(?={self.t})", f"{self.a}", f"#{string}#").strip('#')

soundchanger/change.py

@@ -0,0 +1,47 @@
+import re
+
+
+def apply(change, string, categories=None, apply=True):
+    """Apply a sound change to a given string"""
+
+    if not apply:
+        return string
+
+    # Set up default categories
+    if not categories:
+        categories = {
+            'V': 'aeiou'
+        }
+
+    # Prepare change for regex
+    for k, v in {'{': '[', '}': ']', ',': '', ' ': ''}.items():
+        change = change.replace(k, v)
+    
+    # Replacements for categories
+    for k, v in categories.items():
+        # Replacement of categories inside brackets (before or after a comma)
+        change = re.sub(f'((?<=,){k}|{k}(?=,))', v, change)
+        # Replacements of categories anywhere else
+        change = change.replace(k, f"[{v}]")
+
+    # Check validity of change
+    if change.count('>') != 1:
+        raise ValueError(f"Change {change} is not a valid sound change. (Missing character '>')")
+
+    if change.count('/') > 1:
+        raise ValueError(f"Change {change} is not a valid sound change. (More than one '/' character)")
+
+    if '/' in change:
+        change, environment = change.split('/')
+    else:
+        environment = '._.'
+
+    if environment.count('_') != 1:
+        raise ValueError(f"Environment {environment} is not a valid environment. (Character '_' should exist exactly once)")
+
+    original, repl = change.split('>')
+    before, after = environment.split('_')
+
+    pattern = f"(?<={before}){original}(?={after})"
+    print(pattern)
+    return re.sub(pattern, repl, f"#{string}#").strip('#')

tests/test_apply.py

@@ -1,24 +0,0 @@
-from soundchanger import Change
-
-
-def test_simple_change_without_environment():
-    c = Change('p>f')
-    assert c.sub('pana') == 'fana'
-    assert c.sub('kapa') == 'kafa'
-
-def test_simple_change_with_environment():
-    c = Change('p>f/#_a')
-    assert c.sub('pana') == 'fana'
-    assert c.sub('pune') == 'pune'
-    assert c.sub('kapa') == 'kapa'
-
-def test_complex_change_with_environment():
-    c = Change('p>f/{#,a}_{a,u}')
-    assert c.sub('pana') == 'fana'
-    assert c.sub('pune') == 'fune'
-    assert c.sub('kapa') == 'kafa'
-
-# def test_simple_change_with_category():
-#     c = Change('w>h/V_V')
-#     assert c.sub('kawa') == 'kaha'
-#     assert c.sub('tuwo') == 'tuho'

tests/test_change.py

@@ -0,0 +1,25 @@
+from soundchanger.change import apply
+
+
+def test_apply_without_environment():
+    assert apply('p>h', 'pana') == 'hana'
+
+def test_apply_with_environment():
+    assert apply('p>f/#_u', 'pune') == 'fune'
+
+def test_apply_with_complex_environment():
+    inputs =  ['pana', 'pina', 'puna', 'pama', 'pima', 'puma']
+    outputs = ['pana', 'hina', 'huna', 'pama', 'hima', 'huma']
+    for string, output in zip(inputs, outputs):
+        assert apply(
+                change='p>h/#_{u,i}Na#',
+                string=string,
+                categories={'N': 'nm'}
+            ) == output
+
+def test_apply_with_complex_group_and_categories():
+    assert apply('e>i/{#,p,t,k}V{m,n,h}_#', 'pane', categories={
+        'V': 'aiu',
+        'P': 'ptk',
+        'N': 'mn',
+        }) == 'pani'

tests/test_change_errors.py

@@ -0,0 +1,15 @@
+import pytest
+import re
+from soundchanger.change import apply
+
+def test_parse_change_error_change():
+    with pytest.raises(ValueError, match=re.escape("Change  is not a valid sound change. (Missing character '>')")):
+        apply('', '')
+
+def test_apply_error_split():
+    with pytest.raises(ValueError, match=re.escape("Change a>b/c/d is not a valid sound change. (More than one '/' character)")):
+        apply('a>b/c/d', '')
+
+def test_apply_error_environment():
+    with pytest.raises(ValueError, match=re.escape("Environment c is not a valid environment. (Character '_' should exist exactly once)")):
+        apply('a>b/c', '')