(lambda file:(lambda file, pos: [len(file.read(1)) == 0, file.seek(pos)][0])(file, file.tell()))
Lambda returns if file is at eof
#How it works:
len(file.read(1)) == 0
Trys to read one character and checks if the returned string has a length of 0 (if you read a file at eof you get a zero length string).