printer.py: fix typos
diff --git a/sympy/printing/printer.py b/sympy/printing/printer.py
--- a/sympy/printing/printer.py
+++ b/sympy/printing/printer.py
@@ -22,7 +22,7 @@ class Printer(object):
 
        Also, if BAR is a subclass of FOO, _print_FOO(bar) will be called for
        instance of BAR, if no _print_BAR is provided.  Thus, usually, we don't
-       need to provide prining routines for every class we want to support --
+       need to provide printing routines for every class we want to support --
        only generic routine has to be provided for a set of classes. 
 
        A good example for this are functions - for example PrettyPrinter only
@@ -52,7 +52,7 @@ class Printer(object):
            It's job is to loop through expr classes (class + it's bases), and
            try to dispatch the work to _print_<EXPR_CLASS>
 
-           e.g., suppose we have the following class hierarcy::
+           e.g., suppose we have the following class hierarchy::
 
                  Basic
                    |