import shutil
which_wakeonlan = shutil.which("wakeonlan")

Also

# simple path search
import os
path = os.getenv("PATH")
ps = path.split(":")
n = "bobbins"
for x in ps:
  if os.path.isfile(os.path.join(x,n)) and os.access(os.path.join(x,n), os.X_OK):
    print(os.path.join(x,n))
    break

# is executable in path
# from https://stackoverflow.com/questions/377017/test-if-executable-exists-in-python
my_command = 'ls'
x = any(
    (
        os.access(os.path.join(path, my_command), os.X_OK) 
        and os.path.isfile(os.path.join(path, my_command))
    )
    for path in os.environ["PATH"].split(os.pathsep)
)
if x:
  print("found",my_command)

import shutil
print(shutil.which("ls"))

Note any(xs) returns True if any element of the iterable xs is True, else False.