added eprint

cs50/cs50.py

@@ -1,4 +1,5 @@
 from __future__ import print_function
+import inspect
 import re
 import sys
 
@@ -20,6 +21,17 @@ def write(self, x):
 sys.stderr = flushfile(sys.stderr)
 sys.stdout = flushfile(sys.stdout)
 
+def eprint(*args, **kwargs):
+    """
+    Print an error message to standard error, prefixing it with
+    file name and line number from which method was called.
+    """
+    end = kwargs.get("end", "\n")
+    sep = kwargs.get("sep", " ")
+    (filename, lineno) = inspect.stack()[1][1:3]
+    print("{}:{}: ".format(filename, lineno), end="")
+    print(*args, end=end, file=sys.stderr, sep=sep)
+
 def get_char(prompt=None):
     """
     Read a line of text from standard input and return the equivalent char;