Shebang detection improvements (#438)

* Recognize python with arguments in shebang

* Recognize python with d/m/u suffix in shebang

https://www.python.org/dev/peps/pep-3149/#proposal

* Recognize python with minor version in shebang

* Avoid unnecessary line splitting in shebang search

* Add test for python shebang-like not on the first line

2 files changed, 29 insertions, 4 deletions

diff --git a/pyflakes/api.py b/pyflakes/api.py
index 6226e5d..50e8ad8 100644
--- a/pyflakes/api.py
+++ b/pyflakes/api.py
@@ -14,7 +14,7 @@ from pyflakes import reporter as modReporter
 
 __all__ = ['check', 'checkPath', 'checkRecursive', 'iterSourceCode', 'main']
 
-PYTHON_SHEBANG_REGEX = re.compile(br'^#!.*\bpython[23w]?\b\s*$')
+PYTHON_SHEBANG_REGEX = re.compile(br'^#!.*\bpython([23](\.\d+)?|w)?[dmu]?\s')
 
 
 def check(codeString, filename, reporter=None):
@@ -118,8 +118,7 @@ def isPythonFile(filename):
     except IOError:
         return False
 
-    first_line = text.splitlines()[0]
-    return PYTHON_SHEBANG_REGEX.match(first_line)
+    return PYTHON_SHEBANG_REGEX.match(text)
 
 
 def iterSourceCode(paths):
diff --git a/pyflakes/test/test_api.py b/pyflakes/test/test_api.py
index ee205f9..93b3886 100644
--- a/pyflakes/test/test_api.py
+++ b/pyflakes/test/test_api.py
@@ -214,9 +214,35 @@ class TestIterSourceCode(TestCase):
         with open(pythonw, 'w') as fd:
             fd.write('#!/usr/bin/env pythonw\n')
 
+        python3args = os.path.join(self.tempdir, 'g')
+        with open(python3args, 'w') as fd:
+            fd.write('#!/usr/bin/python3 -u\n')
+
+        python2u = os.path.join(self.tempdir, 'h')
+        with open(python2u, 'w') as fd:
+            fd.write('#!/usr/bin/python2u\n')
+
+        python3d = os.path.join(self.tempdir, 'i')
+        with open(python3d, 'w') as fd:
+            fd.write('#!/usr/local/bin/python3d\n')
+
+        python38m = os.path.join(self.tempdir, 'j')
+        with open(python38m, 'w') as fd:
+            fd.write('#! /usr/bin/env python3.8m\n')
+
+        python27 = os.path.join(self.tempdir, 'k')
+        with open(python27, 'w') as fd:
+            fd.write('#!/usr/bin/python2.7   \n')
+
+        # Should NOT be treated as Python source
+        notfirst = os.path.join(self.tempdir, 'l')
+        with open(notfirst, 'w') as fd:
+            fd.write('#!/bin/sh\n#!/usr/bin/python\n')
+
         self.assertEqual(
             sorted(iterSourceCode([self.tempdir])),
-            sorted([python, python2, python3, pythonw]))
+            sorted([python, python2, python3, pythonw, python3args, python2u,
+                    python3d, python38m, python27]))
 
     def test_multipleDirectories(self):
         """