Add flake8 and fix warnings

Pipfile

@@ -4,6 +4,9 @@ url = "https://pypi.python.org/simple"
 name = "pypi"
 verify_ssl = true
 
+[scripts]
+
+lint = "flake8 nbcollate"
 
 [dev-packages]
 
@@ -13,6 +16,10 @@ keyring = "*"
 Sphinx = "*"
 bumpversion = "*"
 sphinx_rtd_theme = "*"
+flake8 = "*"
+mccabe = "*"
+pycodestyle = "==2.3.1"  # newer versions are incompatible with flake8 https://github.com/PyCQA/pycodestyle/issues/741
+pyflakes = "*"
 
 
 [packages]

nbcollate/nbcollate.py

@@ -14,6 +14,8 @@
 from difflib import SequenceMatcher
 from itertools import starmap
 
+import nbformat
+
 # QUESTION_RE = r'#+ (Exercise|Question)'
 SOURCE_METADATA_KEY = 'nbcollate_source'
 
@@ -87,16 +89,17 @@ def nbcollate(assignment_nb, answer_nbs, *, ids=None, labels=None, clear_outputs
 
 
 def make_label_cell(label):
-    "Create a cell that labels a collated notebook with ``label``."
+    """Create a cell that labels a collated notebook with ``label``."""
     return nbformat.v4.new_markdown_cell(source='**{}**'.format(label))
 
 
 def cell_strings(nb):
-    "Return a cell's normalized source, for comparison."
+    """Return a cell's normalized source, for comparison."""
     return [cell.source.strip() for cell in nb.cells]
 
 
 def NotebookMatcher(nb1, nb2):
+    """A SequenceMatcher whose sequences are the notebook cell strings."""
     return SequenceMatcher(None, cell_strings(nb1), cell_strings(nb2))
 
 
@@ -149,15 +152,14 @@ def sort_answers(nb):
     Args:
         nb (Notebook): A Jupyter notebook. This is modified in place.
     """
-    dups = []
     out = []
     for _, cells in i_sections(nb):
         out += sorted(cells, key=lambda c: (len(c.source.strip().splitlines()), c.source.strip()))
     nb.cells = out
 
 
 def get_cell_source_id(cell):
-    "Return an answer notebook id that was placed in a cell by :func:`nbcollate`."
+    """Return an answer notebook id that was placed in a cell by :func:`nbcollate`."""
     return getattr(cell.metadata, SOURCE_METADATA_KEY, None)
 
 

requirements.txt

@@ -1 +1,3 @@
-nbformat~=4.4.0
+# ReadTheDocs.org uses this
+
+nbformat~=4.4

setup.cfg

@@ -8,15 +8,6 @@ test = pytest
 
 [bumpversion:file:nbcollate/__init__.py]
 
-[pep8]
-max-line-length = 160
-
 [flake8]
 max-line-length = 160
-ignore = D100,D101,D102,D103,D104,H101,H301,H306
 exclude = nbcollate/__init__.py,tests
-
-[yapf]
-based_on_style = pep8                                                                     │XlsxWriter (1.0.0)
-column_limit = 120
-