You have to put the python path in the PATH
variable.
In the System Variables section, you should have User Variables and System Variables. Search for the PATH
variable and edit its value, adding at the end ;C:\python27
.
The ;
is to tell the variable to add a new path to this value, and the rest, is just to tell which path that is.
On the other hand, you can use ;%python%
to add the variable you created.