Count number of files with certain extension in Python

I am fairly new to Python and I am trying to figure out the most efficient way to count the number of .TIF files in a particular sub-directory.

Doing some searching, I found one example (I have not tested), which claimed to count all of the files in a directory:

file_count = sum((len(f) for _, _, f in os.walk(myPath)))

This is fine, but I need to only count TIF files. My directory will contain other files types, but I only want to count TIFs.

Currently I am using the following code:

tifCounter = 0
for root, dirs, files in os.walk(myPath):
    for file in files:    
        if file.endswith('.tif'):
            tifCounter += 1

It works fine, but the looping seems to be excessive/expensive to me. Any way to do this more efficiently?

Thanks.