Make Graham Scan in Python PEP8 compliant (algorithm-archivists#644)

* Rename Graham Scan in Python according to PEP8

* Apply black to Graham Scan in Python

* Turn code comments into docstrings

Author: berquist

contents/graham_scan/code/python/grahamScan.py

@@ -0,0 +1,56 @@
+from math import atan2
+
+
+def counter_clockwise(p1, p2, p3):
+    """Is the turn counter-clockwise?"""
+    return (p3[1] - p1[1]) * (p2[0] - p1[0]) >= (p2[1] - p1[1]) * (p3[0] - p1[0])
+
+
+def polar_angle(ref, point):
+    """Find the polar angle of a point relative to a reference point"""
+    return atan2(point[1] - ref[1], point[0] - ref[0])
+
+
+def graham_scan(gift):
+    gift = list(set(gift))  # Remove duplicate points
+    start = min(gift, key=lambda p: (p[1], p[0]))  # Must be in hull
+    gift.remove(start)
+
+    s = sorted(gift, key=lambda point: polar_angle(start, point))
+    hull = [start, s[0], s[1]]
+
+    # Remove points from hull that make the hull concave
+    for pt in s[2:]:
+        while not counter_clockwise(hull[-2], hull[-1], pt):
+            del hull[-1]
+        hull.append(pt)
+
+    return hull
+
+
+def main():
+    test_gift = [
+        (-5, 2),
+        (5, 7),
+        (-6, -12),
+        (-14, -14),
+        (9, 9),
+        (-1, -1),
+        (-10, 11),
+        (-6, 15),
+        (-6, -8),
+        (15, -9),
+        (7, -7),
+        (-2, -9),
+        (6, -5),
+        (0, 14),
+        (2, 8),
+    ]
+    hull = graham_scan(test_gift)
+
+    print("The points in the hull are:")
+    for point in hull:
+        print(point)
+
+
+main()

contents/graham_scan/code/python/graham_scan.py

@@ -21,7 +21,7 @@ We can find whether a rotation is counter-clockwise with trigonometric functions
 {% sample lang="js" %}
 [import:36-38, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
-[import:4-6, lang:"python"](code/python/grahamScan.py)
+[import:4-6, lang:"python"](code/python/graham_scan.py)
 {% sample lang="go" %}
 [import:13-15, lang:"go"](code/golang/graham.go)
 {% sample lang="java" %}
@@ -51,7 +51,7 @@ In the end, the code should look something like this:
 {% sample lang="js" %}
 [import:1-30, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
-[import:14-27, lang:"python"](code/python/grahamScan.py)
+[import:14-28, lang:"python"](code/python/graham_scan.py)
 {% sample lang="go" %}
 [import:21-42, lang:"go"](code/golang/graham.go)
 {% sample lang="java" %}
@@ -76,7 +76,7 @@ In the end, the code should look something like this:
 {% sample lang="js" %}
 [import, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
-[import, lang:"python"](code/python/grahamScan.py)
+[import, lang:"python"](code/python/graham_scan.py)
 {% sample lang="go" %}
 [import, lang:"go"](code/golang/graham.go)
 {% sample lang="java" %}