Add canvas homework retrieval script

.gitignore

@@ -1 +1,2 @@
 /__pycache__/
+/.canvas_auth

canvas

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+
+import subprocess
+import sys
+import os
+import requests
+
+s = requests.Session()
+# auth should be in a file called '.canvas_auth' in the same dir
+# should be of the form 'Bearer <auth code>'
+with open(os.path.dirname(os.path.realpath(__file__)) + '/.canvas_auth') as f:
+    s.headers.update({"Authorization": f.read().strip()})
+
+def do_update():
+    courses = s.get("https://canvas.wpi.edu/api/v1/courses",
+                    params={'enrollment_state': 'active'}).json()
+
+    did_change = False
+    for course in courses:
+        assignments = s.get(
+            f"https://canvas.wpi.edu/api/v1/courses/{course['id']}/assignments",
+            params={'bucket': 'future'}).json()
+        for assignment in assignments:
+            if assignment['due_at'] is not None:
+                course_code = course['course_code'].split('-')[0]
+                date_str = assignment['due_at'][:10] # just take %Y-%m-%d
+                todo_string = f"(B) +hw class:{course_code} {assignment['name']} due:{date_str}"
+
+                command = ["todo.sh", "listall", todo_string]
+                lines = subprocess.check_output(command).decode(encoding='UTF-8').split('\n')[:-5]
+                if len(lines) < 1: # doesn't exist in todo.txt yet
+                    subprocess.call(["todo.sh", "add", todo_string])
+                    did_change = True
+
+    if not did_change:
+        print("No changes to make")
+
+if __name__ == '__main__':
+    if len(sys.argv) == 2 and sys.argv[1] == "usage":
+        print("    canvasUpdate\n"
+              "      Adds all assignments from canvas that do not already exist")
+        exit(0)
+
+    if len(sys.argv) >= 3:
+        print("Too many arguments!")
+        exit(-1)
+    else:
+        do_update()