D401: Allow multiple imperative forms of the same stem. (#382)

* Allow multiple imperative forms of the same stem.

* Update phrasing of violation.

* Select best imperative by longest prefix match

* Fixed test after merge.

* Added line to release notes.

* Code review fixes.

docs/release_notes.rst

@@ -4,6 +4,14 @@ Release Notes
 **pydocstyle** version numbers follow the
 `Semantic Versioning <http://semver.org/>`_ specification.
 
+Current Development Version
+---------------------------
+
+Bug Fixes
+
+* D401: Fixed a false positive where one stem had multiple imperative forms,
+  e.g., init and initialize / initiate (#382).
+
 4.0.0 - July 6th, 2019
 ---------------------------
 

src/pydocstyle/checker.py

@@ -13,7 +13,7 @@
 from .parser import (Package, Module, Class, NestedClass, Definition, AllError,
                      Method, Function, NestedFunction, Parser, StringIO,
                      ParseError)
-from .utils import log, is_blank, pairwise
+from .utils import log, is_blank, pairwise, common_prefix_length
 from .wordlists import IMPERATIVE_VERBS, IMPERATIVE_BLACKLIST, stem
 
 
@@ -440,16 +440,20 @@ def check_imperative_mood(self, function, docstring):  # def context
                     return violations.D401b(first_word)
 
                 try:
-                    correct_form = IMPERATIVE_VERBS.get(stem(check_word))
+                    correct_forms = IMPERATIVE_VERBS.get(stem(check_word))
                 except UnicodeDecodeError:
                     # This is raised when the docstring contains unicode
                     # characters in the first word, but is not a unicode
                     # string. In which case D302 will be reported. Ignoring.
                     return
 
-                if correct_form and correct_form != check_word:
+                if correct_forms and check_word not in correct_forms:
+                    best = max(
+                        correct_forms,
+                        key=lambda f: common_prefix_length(check_word, f)
+                    )
                     return violations.D401(
-                        correct_form.capitalize(),
+                        best.capitalize(),
                         first_word
                     )
 

src/pydocstyle/utils.py

@@ -25,3 +25,16 @@ def pairwise(
     a, b = tee(iterable)
     _ = next(b, default_value)
     return zip_longest(a, b, fillvalue=default_value)
+
+
+def common_prefix_length(a: str, b: str) -> int:
+    """Return the length of the longest common prefix of a and b.
+
+    >>> common_prefix_length('abcd', 'abce')
+    3
+
+    """
+    for common, (ca, cb) in enumerate(zip(a, b)):
+        if ca != cb:
+            return common
+    return min(len(a), len(b))

src/pydocstyle/violations.py

@@ -125,7 +125,7 @@ def create_error(
                 self,
                 error_code: str,
                 error_desc: str,
-                error_context: Optional[str]=None,
+                error_context: Optional[str] = None,
         ) -> Callable[[Iterable[str]], Error]:
             """Create an error, register it to this group and return it."""
             # TODO: check prefix
@@ -219,7 +219,7 @@ def to_rst(cls) -> str:
 D400 = D4xx.create_error('D400', 'First line should end with a period',
                          'not {0!r}')
 D401 = D4xx.create_error('D401', 'First line should be in imperative mood',
-                         "'{0}', not '{1}'")
+                         "perhaps '{0}', not '{1}'")
 D401b = D4xx.create_error('D401', 'First line should be in imperative mood; '
                           'try rephrasing', "found '{0}'")
 D402 = D4xx.create_error('D402', 'First line should not be the function\'s '

src/pydocstyle/wordlists.py

@@ -7,7 +7,7 @@
 import re
 import pkgutil
 import snowballstemmer
-from typing import Iterator
+from typing import Iterator, Dict, Set
 
 
 #: Regular expression for stripping comments from the wordlists
@@ -36,7 +36,14 @@ def load_wordlist(name: str) -> Iterator[str]:
 
 
 #: A dict mapping stemmed verbs to the imperative form
-IMPERATIVE_VERBS = {stem(v): v for v in load_wordlist('imperatives.txt')}
+def make_imperative_verbs_dict(wordlist: Iterator[str]) -> Dict[str, Set[str]]:
+    imperative_verbs = {}  # type: Dict[str, Set[str]]
+    for word in wordlist:
+        imperative_verbs.setdefault(stem(word), set()).add(word)
+    return imperative_verbs
+
+
+IMPERATIVE_VERBS = make_imperative_verbs_dict(load_wordlist('imperatives.txt'))
 
 #: Words that are forbidden to appear as the first word in a docstring
 IMPERATIVE_BLACKLIST = set(load_wordlist('imperatives_blacklist.txt'))

src/tests/test_cases/noqa.py

@@ -16,7 +16,8 @@ def docstring_bad_ignore_one():  # noqa: D400,D401,D415
     pass
 
 
-@expect("D401: First line should be in imperative mood ('Run', not 'Runs')")
+@expect("D401: First line should be in imperative mood "
+        "(perhaps 'Run', not 'Runs')")
 def docstring_ignore_some_violations_but_catch_D401():  # noqa: E501,D400,D415
     """Runs something"""
     pass

src/tests/test_cases/sections.py

@@ -177,7 +177,7 @@ def ignore_non_actual_section():  # noqa: D416
 
 @expect(_D213)
 @expect("D401: First line should be in imperative mood "
-        "('Return', not 'Returns')")
+        "(perhaps 'Return', not 'Returns')")
 @expect("D400: First line should end with a period (not 's')")
 @expect("D415: First line should end with a period, question "
         "mark, or exclamation point (not 's')")

src/tests/test_cases/test.py

@@ -287,8 +287,8 @@ def lwnlkjl():
     """Summary"""
 
 
-@expect("D401: First line should be in imperative mood ('Return', not "
-        "'Returns')")
+@expect("D401: First line should be in imperative mood "
+        "(perhaps 'Return', not 'Returns')")
 def liouiwnlkjl():
     """Returns foo."""
 
@@ -361,7 +361,8 @@ def inner_function():
 
 
 @expect("D400: First line should end with a period (not 'g')")
-@expect("D401: First line should be in imperative mood ('Run', not 'Runs')")
+@expect("D401: First line should be in imperative mood "
+        "(perhaps 'Run', not 'Runs')")
 @expect("D415: First line should end with a period, question mark, "
         "or exclamation point (not 'g')")
 def docstring_bad():
@@ -379,12 +380,29 @@ def docstring_bad_ignore_one():  # noqa: D400,D401,D415
     pass
 
 
-@expect("D401: First line should be in imperative mood ('Run', not 'Runs')")
+@expect("D401: First line should be in imperative mood "
+        "(perhaps 'Run', not 'Runs')")
 def docstring_ignore_some_violations_but_catch_D401():  # noqa: E501,D400,D415
     """Runs something"""
     pass
 
 
+@expect(
+    "D401: First line should be in imperative mood "
+    "(perhaps 'Initiate', not 'Initiates')"
+)
+def docstring_initiates():
+    """Initiates the process."""
+
+
+@expect(
+    "D401: First line should be in imperative mood "
+    "(perhaps 'Initialize', not 'Initializes')"
+)
+def docstring_initializes():
+    """Initializes the process."""
+
+
 @wraps(docstring_bad_ignore_one)
 def bad_decorated_function():
     """Bad (E501) but decorated"""

src/tests/test_utils.py

@@ -0,0 +1,28 @@
+"""Unit test for pydocstyle utils.
+
+Use tox or py.test to run the test suite.
+"""
+from pydocstyle import utils
+
+
+__all__ = ()
+
+
+def test_common_prefix():
+    """Test common prefix length of two strings."""
+    assert utils.common_prefix_length('abcd', 'abce') == 3
+
+
+def test_no_common_prefix():
+    """Test common prefix length of two strings that have no common prefix."""
+    assert utils.common_prefix_length('abcd', 'cdef') == 0
+
+
+def test_differ_length():
+    """Test common prefix length of two strings differing in length."""
+    assert utils.common_prefix_length('abcd', 'ab') == 2
+
+
+def test_empty_string():
+    """Test common prefix length of two strings, one of them empty."""
+    assert utils.common_prefix_length('abcd', '') == 0