In some cases exception-way could be much faster

check_file_exists.py

from __future__ import print_function

import os
import timeit

test1="""
def check_file_classic():
    if os.path.exists("asdfas"):
        return 1
    return 2
"""

test2="""
def check_file_with_exception():
    try:
        open("asdfas")
    except:
        return 2
"""

iterations=10000

print("Classic")
print(">>", timeit.timeit(test1, number=iterations))
print("Exception")
print(">>", timeit.timeit(test2, number=iterations))