Merge branch 'develop' into eprint

cs50/cs50.py

@@ -32,8 +32,12 @@ def eprint(*args, **kwargs):
     print("{}:{}: ".format(filename, lineno), end="")
     print(*args, end=end, file=sys.stderr, sep=sep)
 
-def get_char():
-    """Read a line of text from standard input and return the equivalent char."""
+def get_char(prompt=None):
+    """
+    Read a line of text from standard input and return the equivalent char;
+    if text is not a single char, user is prompted to retry. If line can't
+    be read, return None.
+    """
     while True:
         s = get_string(prompt)
         if s is None: