compatible image type

[gordon]

hi
in my application a file selection by user returns a pathname string
like F:/images/png/my.png  or F:/docs/text/somedoc.txt ....etc.
I can get the extension using
extn=string.split(os.path.basename(pathname),'.' )[1]

then later on i want to create a Photoimage using

ImageTk.PhotoImage(file=pathname) and display it on a canvas.

the extn can be anything ..even zip or bat ,doc whatever depending on
user selection...I want to put someway to raise an error message to
the user if he selects a file with extension not of a compatible image
type for PhotoImage.How should i do this? should i check 'extn' to a
list of compatible image type extensions(something like
[''jpg','jpeg','png','gif'...] )  or is there a better way?

gordon