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с so: Python 3.7.2 (default, Jan 3 2019, 02:55:40) IPython 5.8.0 Intel(R) Core(TM) i5-4590T CPU @ 2.00GHz In [1]: %timeit root = "sample"; output = "output"; path = "{}/{}".format(root, output) The slowest run took 12.44 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 5: 223 ns per loop In [2]: %timeit root = "sample"; output = "output"; path = root + '/' + output The slowest run took 13.82 times longer than the fastest. This could mean that an intermediate result is being cached. 10000000 loops, best of 5: 101 ns per loop In [3]: %timeit root = "sample"; output = "output"; path = "%s/%s" % (root, output) The slowest run took 27.97 times longer than the fastest. This could mean that an intermediate result is being cached. 10000000 loops, best of 5: 155 ns per loop In [4]: %timeit root = "sample"; output = "output"; path = f"{root}/{output}" The slowest run took 19.52 times longer than the fastest. This could mean that an intermediate result is being cached. 10000000 loops, best of 5: 77.8 ns per loop